def run_model(args, currentmodelrun, modelend, numbermodelruns, inputfile, usernamespace):
"""Runs a model - processes the input file; builds the Yee cells; calculates update coefficients; runs main FDTD loop.
Args:
args (dict): Namespace with command line arguments
currentmodelrun (int): Current model run number.
modelend (int): Number of last model to run.
numbermodelruns (int): Total number of model runs.
inputfile (object): File object for the input file.
usernamespace (dict): Namespace that can be accessed by user
in any Python code blocks in input file.
Returns:
tsolve (int): Length of time (seconds) of main FDTD calculations
"""
# Monitor memory usage
p = psutil.Process()
# Declare variable to hold FDTDGrid class
global G
# Used for naming geometry and output files
appendmodelnumber = '' if numbermodelruns == 1 and not args.task and not args.restart else '_'+str(currentmodelrun)
appendmodelnumberGeometry = '' if numbermodelruns == 1 and not args.task and not args.restart or args.geometry_fixed else '_'+str(currentmodelrun)
# Normal model reading/building process; bypassed if geometry information to be reused
if 'G' not in globals():
# Initialise an instance of the FDTDGrid class
G = FDTDGrid()
# Get information about host machine
# (need to save this info to FDTDGrid instance after it has been created)
G.hostinfo = get_host_info()
# Single GPU object
if args.gpu:
G.gpu = args.gpu
G.inputfilename = os.path.split(inputfile.name)[1]
G.inputdirectory = os.path.dirname(os.path.abspath(inputfile.name))
inputfilestr = '\n--- Model {}/{}, input file: {}'.format(currentmodelrun, modelend, inputfile.name)
if G.messages:
print(Fore.GREEN + '{} {}\n'.format(inputfilestr, '-' * (get_terminal_width() - 1 - len(inputfilestr))) + Style.RESET_ALL)
# Add the current model run to namespace that can be accessed by
# user in any Python code blocks in input file
usernamespace['current_model_run'] = currentmodelrun
# Read input file and process any Python and include file commands
processedlines = process_python_include_code(inputfile, usernamespace)
# Print constants/variables in user-accessable namespace
uservars = ''
for key, value in sorted(usernamespace.items()):
if key != '__builtins__':
uservars += '{}: {}, '.format(key, value)
if G.messages:
print('Constants/variables used/available for Python scripting: {{{}}}\n'.format(uservars[:-2]))
# Write a file containing the input commands after Python or include file commands have been processed
if args.write_processed:
write_processed_file(processedlines, appendmodelnumber, G)
# Check validity of command names and that essential commands are present
singlecmds, multicmds, geometry = check_cmd_names(processedlines)
# Create built-in materials
m = Material(0, 'pec')
m.se = float('inf')
m.type = 'builtin'
m.averagable = False
G.materials.append(m)
m = Material(1, 'free_space')
m.type = 'builtin'
G.materials.append(m)
# Process parameters for commands that can only occur once in the model
process_singlecmds(singlecmds, G)
# Process parameters for commands that can occur multiple times in the model
if G.messages: print()
process_multicmds(multicmds, G)
# Estimate and check memory (RAM) usage
G.memory_estimate_basic()
#G.memory_check()
#if G.messages:
# if G.gpu is None:
# print('\nMemory (RAM) required: ~{}\n'.format(human_size(G.memoryusage)))
# else:
# print('\nMemory (RAM) required: ~{} host + ~{} GPU\n'.format(human_size(G.memoryusage), human_size(G.memoryusage)))
# Initialise an array for volumetric material IDs (solid), boolean
# arrays for specifying materials not to be averaged (rigid),
# an array for cell edge IDs (ID)
G.initialise_geometry_arrays()
# Initialise arrays for the field components
if G.gpu is None:
G.initialise_field_arrays()
# Process geometry commands in the order they were given
process_geometrycmds(geometry, G)
# Build the PMLs and calculate initial coefficients
if G.messages: print()
if all(value == 0 for value in G.pmlthickness.values()):
if G.messages:
print('PML: switched off')
pass # If all the PMLs are switched off don't need to build anything
else:
# Set default CFS parameters for PML if not given
if not G.cfs:
G.cfs = [CFS()]
if G.messages:
if all(value == G.pmlthickness['x0'] for value in G.pmlthickness.values()):
pmlinfo = str(G.pmlthickness['x0'])
else:
pmlinfo = ''
for key, value in G.pmlthickness.items():
pmlinfo += '{}: {}, '.format(key, value)
pmlinfo = pmlinfo[:-2] + ' cells'
print('PML: formulation: {}, order: {}, thickness: {}'.format(G.pmlformulation, len(G.cfs), pmlinfo))
pbar = tqdm(total=sum(1 for value in G.pmlthickness.values() if value > 0), desc='Building PML boundaries', ncols=get_terminal_width() - 1, file=sys.stdout, disable=not G.progressbars)
build_pmls(G, pbar)
pbar.close()
# Build the model, i.e. set the material properties (ID) for every edge
# of every Yee cell
if G.messages: print()
pbar = tqdm(total=2, desc='Building main grid', ncols=get_terminal_width() - 1, file=sys.stdout, disable=not G.progressbars)
build_electric_components(G.solid, G.rigidE, G.ID, G)
pbar.update()
build_magnetic_components(G.solid, G.rigidH, G.ID, G)
pbar.update()
pbar.close()
# Add PEC boundaries to invariant direction in 2D modes
# N.B. 2D modes are a single cell slice of 3D grid
if '2D TMx' in G.mode:
# Ey & Ez components
G.ID[1, 0, :, :] = 0
G.ID[1, 1, :, :] = 0
G.ID[2, 0, :, :] = 0
G.ID[2, 1, :, :] = 0
elif '2D TMy' in G.mode:
# Ex & Ez components
G.ID[0, :, 0, :] = 0
G.ID[0, :, 1, :] = 0
G.ID[2, :, 0, :] = 0
G.ID[2, :, 1, :] = 0
elif '2D TMz' in G.mode:
# Ex & Ey components
G.ID[0, :, :, 0] = 0
G.ID[0, :, :, 1] = 0
G.ID[1, :, :, 0] = 0
G.ID[1, :, :, 1] = 0
# Process any voltage sources (that have resistance) to create a new
# material at the source location
for voltagesource in G.voltagesources:
voltagesource.create_material(G)
# Initialise arrays of update coefficients to pass to update functions
G.initialise_std_update_coeff_arrays()
# Initialise arrays of update coefficients and temporary values if
# there are any dispersive materials
if Material.maxpoles != 0:
# Update estimated memory (RAM) usage
G.memoryusage += int(3 * Material.maxpoles * (G.nx + 1) * (G.ny + 1) * (G.nz + 1) * np.dtype(complextype).itemsize)
G.memory_check()
if G.messages:
print('\nMemory (RAM) required - updated (dispersive): ~{}\n'.format(human_size(G.memoryusage)))
G.initialise_dispersive_arrays()
# Check there is sufficient memory to store any snapshots
if G.snapshots:
snapsmemsize = 0
for snap in G.snapshots:
# 2 x required to account for electric and magnetic fields
snapsmemsize += (2 * snap.datasizefield)
G.memoryusage += int(snapsmemsize)
G.memory_check(snapsmemsize=int(snapsmemsize))
if G.messages:
print('\nMemory (RAM) required - updated (snapshots): ~{}\n'.format(human_size(G.memoryusage)))
# Process complete list of materials - calculate update coefficients,
# store in arrays, and build text list of materials/properties
materialsdata = process_materials(G)
if G.messages:
print('\nMaterials:')
materialstable = AsciiTable(materialsdata)
materialstable.outer_border = False
materialstable.justify_columns[0] = 'right'
print(materialstable.table)
# Check to see if numerical dispersion might be a problem
results = dispersion_analysis(G)
if results['error'] and G.messages:
print(Fore.RED + "\nWARNING: Numerical dispersion analysis not carried out as {}".format(results['error']) + Style.RESET_ALL)
elif results['N'] < G.mingridsampling:
raise GeneralError("Non-physical wave propagation: Material '{}' has wavelength sampled by {} cells, less than required minimum for physical wave propagation. Maximum significant frequency estimated as {:g}Hz".format(results['material'].ID, results['N'], results['maxfreq']))
elif results['deltavp'] and np.abs(results['deltavp']) > G.maxnumericaldisp and G.messages:
print(Fore.RED + "\nWARNING: Potentially significant numerical dispersion. Estimated largest physical phase-velocity error is {:.2f}% in material '{}' whose wavelength sampled by {} cells. Maximum significant frequency estimated as {:g}Hz".format(results['deltavp'], results['material'].ID, results['N'], results['maxfreq']) + Style.RESET_ALL)
elif results['deltavp'] and G.messages:
print("\nNumerical dispersion analysis: estimated largest physical phase-velocity error is {:.2f}% in material '{}' whose wavelength sampled by {} cells. Maximum significant frequency estimated as {:g}Hz".format(results['deltavp'], results['material'].ID, results['N'], results['maxfreq']))
# If geometry information to be reused between model runs
else:
inputfilestr = '\n--- Model {}/{}, input file (not re-processed, i.e. geometry fixed): {}'.format(currentmodelrun, modelend, inputfile.name)
if G.messages:
print(Fore.GREEN + '{} {}\n'.format(inputfilestr, '-' * (get_terminal_width() - 1 - len(inputfilestr))) + Style.RESET_ALL)
if G.gpu is None:
# Clear arrays for field components
G.initialise_field_arrays()
# Clear arrays for fields in PML
for pml in G.pmls:
pml.initialise_field_arrays()
# Adjust position of simple sources and receivers if required
if G.srcsteps[0] != 0 or G.srcsteps[1] != 0 or G.srcsteps[2] != 0:
for source in itertools.chain(G.hertziandipoles, G.magneticdipoles):
if currentmodelrun == 1:
if source.xcoord + G.srcsteps[0] * modelend < 0 or source.xcoord + G.srcsteps[0] * modelend > G.nx or source.ycoord + G.srcsteps[1] * modelend < 0 or source.ycoord + G.srcsteps[1] * modelend > G.ny or source.zcoord + G.srcsteps[2] * modelend < 0 or source.zcoord + G.srcsteps[2] * modelend > G.nz:
raise GeneralError('Source(s) will be stepped to a position outside the domain.')
source.xcoord = source.xcoordorigin + (currentmodelrun - 1) * G.srcsteps[0]
source.ycoord = source.ycoordorigin + (currentmodelrun - 1) * G.srcsteps[1]
source.zcoord = source.zcoordorigin + (currentmodelrun - 1) * G.srcsteps[2]
if G.rxsteps[0] != 0 or G.rxsteps[1] != 0 or G.rxsteps[2] != 0:
for receiver in G.rxs:
if currentmodelrun == 1:
if receiver.xcoord + G.rxsteps[0] * modelend < 0 or receiver.xcoord + G.rxsteps[0] * modelend > G.nx or receiver.ycoord + G.rxsteps[1] * modelend < 0 or receiver.ycoord + G.rxsteps[1] * modelend > G.ny or receiver.zcoord + G.rxsteps[2] * modelend < 0 or receiver.zcoord + G.rxsteps[2] * modelend > G.nz:
raise GeneralError('Receiver(s) will be stepped to a position outside the domain.')
receiver.xcoord = receiver.xcoordorigin + (currentmodelrun - 1) * G.rxsteps[0]
receiver.ycoord = receiver.ycoordorigin + (currentmodelrun - 1) * G.rxsteps[1]
receiver.zcoord = receiver.zcoordorigin + (currentmodelrun - 1) * G.rxsteps[2]
# Write files for any geometry views and geometry object outputs
if not (G.geometryviews or G.geometryobjectswrite) and args.geometry_only and G.messages:
print(Fore.RED + '\nWARNING: No geometry views or geometry objects to output found.' + Style.RESET_ALL)
if G.geometryviews and (not args.geometry_fixed or currentmodelrun == 1):
if G.messages: print()
for i, geometryview in enumerate(G.geometryviews):
geometryview.set_filename(appendmodelnumberGeometry, G)
pbar = tqdm(total=geometryview.datawritesize, unit='byte', unit_scale=True, desc='Writing geometry view file {}/{}, {}'.format(i + 1, len(G.geometryviews), os.path.split(geometryview.filename)[1]), ncols=get_terminal_width() - 1, file=sys.stdout, disable=not G.progressbars)
geometryview.write_vtk(G, pbar)
pbar.close()
if G.geometryobjectswrite:
for i, geometryobject in enumerate(G.geometryobjectswrite):
pbar = tqdm(total=geometryobject.datawritesize, unit='byte', unit_scale=True, desc='Writing geometry object file {}/{}, {}'.format(i + 1, len(G.geometryobjectswrite), os.path.split(geometryobject.filename)[1]), ncols=get_terminal_width() - 1, file=sys.stdout, disable=not G.progressbars)
geometryobject.write_hdf5(G, pbar)
pbar.close()
# If only writing geometry information
if args.geometry_only:
tsolve = 0
# Run simulation
else:
# Output filename
inputdirectory, inputfilename = os.path.split(os.path.join(G.inputdirectory, G.inputfilename))
if G.outputdirectory is None:
outputdir = inputdirectory
else:
outputdir = G.outputdirectory
# Save current directory
curdir = os.getcwd()
os.chdir(inputdirectory)
outputdir = os.path.abspath(outputdir)
if not os.path.isdir(outputdir):
os.mkdir(outputdir)
if G.messages:
print('\nCreated output directory: {}'.format(outputdir))
# Restore current directory
os.chdir(curdir)
basename, ext = os.path.splitext(inputfilename)
outputfile = os.path.join(outputdir, basename + appendmodelnumber + '.out')
if G.messages:
print('\nOutput file: {}\n'.format(outputfile))
# Main FDTD solving functions for either CPU or GPU
if G.gpu is None:
tsolve = solve_cpu(currentmodelrun, modelend, G)
else:
tsolve, memsolve = solve_gpu(currentmodelrun, modelend, G)
# Write an output file in HDF5 format
write_hdf5_outputfile(outputfile, G)
# Write any snapshots to file
if G.snapshots:
# Create directory and construct filename from user-supplied name and model run number
snapshotdir = os.path.join(G.inputdirectory, os.path.splitext(G.inputfilename)[0] + '_snaps' + appendmodelnumber)
if not os.path.exists(snapshotdir):
os.mkdir(snapshotdir)
if G.messages: print()
for i, snap in enumerate(G.snapshots):
snap.filename = os.path.abspath(os.path.join(snapshotdir, snap.basefilename + '.vti'))
pbar = tqdm(total=snap.vtkdatawritesize, leave=True, unit='byte', unit_scale=True, desc='Writing snapshot file {} of {}, {}'.format(i + 1, len(G.snapshots), os.path.split(snap.filename)[1]), ncols=get_terminal_width() - 1, file=sys.stdout, disable=not G.progressbars)
snap.write_vtk_imagedata(pbar, G)
pbar.close()
if G.messages: print()
if G.messages:
if G.gpu is None:
print('Memory (RAM) used: ~{}'.format(human_size(p.memory_info().rss)))
else:
print('Memory (RAM) used: ~{} host + ~{} GPU'.format(human_size(p.memory_info().rss), human_size(memsolve)))
print('Solving time [HH:MM:SS]: {}'.format(datetime.timedelta(seconds=tsolve)))
# If geometry information to be reused between model runs then FDTDGrid
# class instance must be global so that it persists
if not args.geometry_fixed or currentmodelrun is modelend:
del G
return tsolve
def run_model(args, modelrun, numbermodelruns, inputfile, usernamespace):
"""Runs a model - processes the input file; builds the Yee cells; calculates update coefficients; runs main FDTD loop.
Args:
args (dict): Namespace with command line arguments
modelrun (int): Current model run number.
numbermodelruns (int): Total number of model runs.
inputfile (str): Name of the input file to open.
usernamespace (dict): Namespace that can be accessed by user in any Python code blocks in input file.
Returns:
tsolve (int): Length of time (seconds) of main FDTD calculations
"""
# Monitor memory usage
p = psutil.Process()
print('\n{}\n\nModel input file: {}\n'.format(68*'*', inputfile))
# Add the current model run to namespace that can be accessed by user in any Python code blocks in input file
usernamespace['current_model_run'] = modelrun
print('Constants/variables available for Python scripting: {}\n'.format(usernamespace))
# Process any user input Python commands
processedlines = python_code_blocks(inputfile, usernamespace)
# Write a file containing the input commands after Python blocks have been processed
if args.write_python:
write_python_processed(inputfile, modelrun, numbermodelruns, processedlines)
# Check validity of command names & that essential commands are present
singlecmds, multicmds, geometry = check_cmd_names(processedlines)
# Initialise an instance of the FDTDGrid class
G = FDTDGrid()
G.inputdirectory = usernamespace['inputdirectory']
# Process parameters for commands that can only occur once in the model
process_singlecmds(singlecmds, multicmds, G)
# Process parameters for commands that can occur multiple times in the model
process_multicmds(multicmds, G)
# Initialise an array for volumetric material IDs (solid), boolean arrays for specifying materials not to be averaged (rigid),
# an array for cell edge IDs (ID), and arrays for the field components.
G.initialise_std_arrays()
# Process the geometry commands in the order they were given
tinputprocstart = perf_counter()
process_geometrycmds(geometry, G)
tinputprocend = perf_counter()
print('\nInput file processed in [HH:MM:SS]: {}'.format(datetime.timedelta(seconds=int(tinputprocend - tinputprocstart))))
# Build the PML and calculate initial coefficients
build_pmls(G)
# Build the model, i.e. set the material properties (ID) for every edge of every Yee cell
tbuildstart = perf_counter()
build_electric_components(G.solid, G.rigidE, G.ID, G)
build_magnetic_components(G.solid, G.rigidH, G.ID, G)
tbuildend = perf_counter()
print('\nModel built in [HH:MM:SS]: {}'.format(datetime.timedelta(seconds=int(tbuildend - tbuildstart))))
# Process any voltage sources (that have resistance) to create a new material at the source location
for voltagesource in G.voltagesources:
voltagesource.create_material(G)
# Initialise arrays of update coefficients to pass to update functions
G.initialise_std_updatecoeff_arrays()
# Initialise arrays of update coefficients and temporary values if there are any dispersive materials
if Material.maxpoles != 0:
G.initialise_dispersive_arrays()
# Calculate update coefficients, store in arrays, and list materials in model
if G.messages:
print('\nMaterials:\n')
print('ID\tName\t\tProperties')
print('{}'.format('-'*50))
for material in G.materials:
# Calculate update coefficients for material
material.calculate_update_coeffsE(G)
material.calculate_update_coeffsH(G)
# Store all update coefficients together
G.updatecoeffsE[material.numID, :] = material.CA, material.CBx, material.CBy, material.CBz, material.srce
G.updatecoeffsH[material.numID, :] = material.DA, material.DBx, material.DBy, material.DBz, material.srcm
# Store coefficients for any dispersive materials
if Material.maxpoles != 0:
z = 0
for pole in range(Material.maxpoles):
G.updatecoeffsdispersive[material.numID, z:z+3] = e0 * material.eqt2[pole], material.eqt[pole], material.zt[pole]
z += 3
if G.messages:
if material.deltaer and material.tau:
tmp = 'delta_epsr={}, tau={} secs; '.format(', '.join('{:g}'.format(deltaer) for deltaer in material.deltaer), ', '.join('{:g}'.format(tau) for tau in material.tau))
else:
tmp = ''
if material.average:
dielectricsmoothing = 'dielectric smoothing permitted.'
else:
dielectricsmoothing = 'dielectric smoothing not permitted.'
print('{:3}\t{:12}\tepsr={:g}, sig={:g} S/m; mur={:g}, sig*={:g} S/m; '.format(material.numID, material.ID, material.er, material.se, material.mr, material.sm) + tmp + dielectricsmoothing)
# Check to see if numerical dispersion might be a problem
if dispersion_check(G.waveforms, G.materials, G.dx, G.dy, G.dz):
print('\nWARNING: Potential numerical dispersion in the simulation. Check the spatial discretisation against the smallest wavelength present.')
# Write files for any geometry views
if not G.geometryviews and args.geometry_only:
raise GeneralError('No geometry views found.')
elif G.geometryviews:
tgeostart = perf_counter()
for geometryview in G.geometryviews:
geometryview.write_file(modelrun, numbermodelruns, G)
tgeoend = perf_counter()
print('\nGeometry file(s) written in [HH:MM:SS]: {}'.format(datetime.timedelta(seconds=int(tgeoend - tgeostart))))
# Run simulation if not doing only geometry
if not args.geometry_only:
# Prepare any snapshot files
for snapshot in G.snapshots:
snapshot.prepare_file(modelrun, numbermodelruns, G)
# Prepare output file
inputfileparts = os.path.splitext(inputfile)
if numbermodelruns == 1:
outputfile = inputfileparts[0] + '.out'
else:
outputfile = inputfileparts[0] + str(modelrun) + '.out'
sys.stdout.write('\nOutput to file: {}\n'.format(outputfile))
sys.stdout.flush()
f = prepare_output_file(outputfile, G)
# Adjust position of sources and receivers if required
if G.srcstepx > 0 or G.srcstepy > 0 or G.srcstepz > 0:
for source in itertools.chain(G.hertziandipoles, G.magneticdipoles, G.voltagesources, G.transmissionlines):
source.xcoord += (modelrun - 1) * G.srcstepx
source.ycoord += (modelrun - 1) * G.srcstepy
source.zcoord += (modelrun - 1) * G.srcstepz
if G.rxstepx > 0 or G.rxstepy > 0 or G.rxstepz > 0:
for receiver in G.rxs:
receiver.xcoord += (modelrun - 1) * G.rxstepx
receiver.ycoord += (modelrun - 1) * G.rxstepy
receiver.zcoord += (modelrun - 1) * G.rxstepz
##################################
# Main FDTD calculation loop #
##################################
tsolvestart = perf_counter()
# Absolute time
abstime = 0
for timestep in range(G.iterations):
if timestep == 0:
tstepstart = perf_counter()
# Write field outputs to file
write_output(f, timestep, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz, G)
# Write any snapshots to file
for snapshot in G.snapshots:
if snapshot.time == timestep + 1:
snapshot.write_snapshot(G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz, G)
# Update electric field components
if Material.maxpoles == 0: # All materials are non-dispersive so do standard update
update_electric(G.nx, G.ny, G.nz, G.nthreads, G.updatecoeffsE, G.ID, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz)
elif Material.maxpoles == 1: # If there are any dispersive materials do 1st part of dispersive update (it is split into two parts as it requires present and updated electric field values).
update_electric_dispersive_1pole_A(G.nx, G.ny, G.nz, G.nthreads, G.updatecoeffsE, G.updatecoeffsdispersive, G.ID, G.Tx, G.Ty, G.Tz, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz)
elif Material.maxpoles > 1:
update_electric_dispersive_multipole_A(G.nx, G.ny, G.nz, G.nthreads, Material.maxpoles, G.updatecoeffsE, G.updatecoeffsdispersive, G.ID, G.Tx, G.Ty, G.Tz, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz)
# Update electric field components with the PML correction
update_electric_pml(G)
# Update electric field components from sources
for voltagesource in G.voltagesources:
voltagesource.update_electric(abstime, G.updatecoeffsE, G.ID, G.Ex, G.Ey, G.Ez, G)
for transmissionline in G.transmissionlines:
transmissionline.update_electric(abstime, G.Ex, G.Ey, G.Ez, G)
for hertziandipole in G.hertziandipoles: # Update any Hertzian dipole sources last
hertziandipole.update_electric(abstime, G.updatecoeffsE, G.ID, G.Ex, G.Ey, G.Ez, G)
# If there are any dispersive materials do 2nd part of dispersive update (it is split into two parts as it requires present and updated electric field values). Therefore it can only be completely updated after the electric field has been updated by the PML and source updates.
if Material.maxpoles == 1:
update_electric_dispersive_1pole_B(G.nx, G.ny, G.nz, G.nthreads, G.updatecoeffsdispersive, G.ID, G.Tx, G.Ty, G.Tz, G.Ex, G.Ey, G.Ez)
elif Material.maxpoles > 1:
update_electric_dispersive_multipole_B(G.nx, G.ny, G.nz, G.nthreads, Material.maxpoles, G.updatecoeffsdispersive, G.ID, G.Tx, G.Ty, G.Tz, G.Ex, G.Ey, G.Ez)
# Increment absolute time value
abstime += 0.5 * G.dt
# Update magnetic field components
update_magnetic(G.nx, G.ny, G.nz, G.nthreads, G.updatecoeffsH, G.ID, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz)
# Update magnetic field components with the PML correction
update_magnetic_pml(G)
# Update magnetic field components from sources
for transmissionline in G.transmissionlines:
transmissionline.update_magnetic(abstime, G.Hx, G.Hy, G.Hz, G)
for magneticdipole in G.magneticdipoles:
magneticdipole.update_magnetic(abstime, G.updatecoeffsH, G.ID, G.Hx, G.Hy, G.Hz, G)
# Increment absolute time value
abstime += 0.5 * G.dt
# Calculate time for two iterations, used to estimate overall runtime
if timestep == 1:
tstepend = perf_counter()
runtime = datetime.timedelta(seconds=int((tstepend - tstepstart) / 2 * G.iterations))
sys.stdout.write('Estimated runtime [HH:MM:SS]: {}\n'.format(runtime))
sys.stdout.write('Solving for model run {} of {}...\n'.format(modelrun, numbermodelruns))
sys.stdout.flush()
elif timestep > 1:
update_progress((timestep + 1) / G.iterations)
# Close output file
f.close()
tsolveend = perf_counter()
print('\n\nSolving took [HH:MM:SS]: {}'.format(datetime.timedelta(seconds=int(tsolveend - tsolvestart))))
print('Peak memory (approx) used: {}'.format(human_size(p.memory_info().rss)))
return int(tsolveend - tsolvestart)
def run_model(args, modelrun, numbermodelruns, inputfile, usernamespace):
"""Runs a model - processes the input file; builds the Yee cells; calculates update coefficients; runs main FDTD loop.
Args:
args (dict): Namespace with command line arguments
modelrun (int): Current model run number.
numbermodelruns (int): Total number of model runs.
inputfile (str): Name of the input file to open.
usernamespace (dict): Namespace that can be accessed by user in any Python code blocks in input file.
"""
# Monitor memory usage
p = psutil.Process()
print('\n{}\n\nModel input file: {}\n'.format(68 * '*', inputfile))
# Add the current model run to namespace that can be accessed by user in any Python code blocks in input file
usernamespace['current_model_run'] = modelrun
print('Constants/variables available for Python scripting: {}\n'.format(
usernamespace))
# Process any user input Python commands
processedlines = python_code_blocks(inputfile, usernamespace)
# Write a file containing the input commands after Python blocks have been processed
if args.write_python:
write_python_processed(inputfile, modelrun, numbermodelruns,
processedlines)
# Check validity of command names & that essential commands are present
singlecmds, multicmds, geometry = check_cmd_names(processedlines)
# Initialise an instance of the FDTDGrid class
G = FDTDGrid()
G.inputdirectory = usernamespace['inputdirectory']
# Process parameters for commands that can only occur once in the model
process_singlecmds(singlecmds, multicmds, G)
# Process parameters for commands that can occur multiple times in the model
process_multicmds(multicmds, G)
# Initialise an array for volumetric material IDs (solid), boolean arrays for specifying materials not to be averaged (rigid),
# an array for cell edge IDs (ID), and arrays for the field components.
G.initialise_std_arrays()
# Process the geometry commands in the order they were given
tinputprocstart = perf_counter()
process_geometrycmds(geometry, G)
tinputprocend = perf_counter()
print('\nInput file processed in [HH:MM:SS]: {}'.format(
datetime.timedelta(seconds=int(tinputprocend - tinputprocstart))))
# Build the PML and calculate initial coefficients
build_pml(G)
# Build the model, i.e. set the material properties (ID) for every edge of every Yee cell
tbuildstart = perf_counter()
build_electric_components(G.solid, G.rigidE, G.ID, G)
build_magnetic_components(G.solid, G.rigidH, G.ID, G)
tbuildend = perf_counter()
print('\nModel built in [HH:MM:SS]: {}'.format(
datetime.timedelta(seconds=int(tbuildend - tbuildstart))))
# Process any voltage sources (that have resistance) to create a new material at the source location
for voltagesource in G.voltagesources:
voltagesource.create_material(G)
# Initialise arrays of update coefficients to pass to update functions
G.initialise_std_updatecoeff_arrays(len(G.materials))
# Initialise arrays of update coefficients and temporary values if there are any dispersive materials
if Material.maxpoles != 0:
G.initialise_dispersive_arrays(len(G.materials))
# Calculate update coefficients, store in arrays, and list materials in model
if G.messages:
print('\nMaterials:\n')
print('ID\tName\t\tProperties')
print('{}'.format('-' * 50))
for material in G.materials:
# Calculate update coefficients for material
material.calculate_update_coeffsE(G)
material.calculate_update_coeffsH(G)
# Store all update coefficients together
G.updatecoeffsE[
material.
numID, :] = material.CA, material.CBx, material.CBy, material.CBz, material.srce
G.updatecoeffsH[
material.
numID, :] = material.DA, material.DBx, material.DBy, material.DBz, material.srcm
# Store coefficients for any dispersive materials
if Material.maxpoles != 0:
z = 0
for pole in range(Material.maxpoles):
G.updatecoeffsdispersive[
material.numID,
z:z + 3] = e0 * material.eqt2[pole], material.eqt[
pole], material.zt[pole]
z += 3
if G.messages:
if material.deltaer and material.tau:
tmp = 'delta_epsr={}, tau={} secs; '.format(
', '.join('{:g}'.format(deltaer)
for deltaer in material.deltaer),
', '.join('{:g}'.format(tau) for tau in material.tau))
else:
tmp = ''
if material.average:
dielectricsmoothing = 'dielectric smoothing permitted.'
else:
dielectricsmoothing = 'dielectric smoothing not permitted.'
print(
'{:3}\t{:12}\tepsr={:g}, sig={:g} S/m; mur={:g}, sig*={:g} S/m; '
.format(material.numID, material.ID, material.er, material.se,
material.mr, material.sm) + tmp + dielectricsmoothing)
# Check to see if numerical dispersion might be a problem
if dispersion_check(G.waveforms, G.materials, G.dx, G.dy, G.dz):
print(
'\nWARNING: Potential numerical dispersion in the simulation. Check the spatial discretisation against the smallest wavelength present.'
)
# Write files for any geometry views
if not G.geometryviews and args.geometry_only:
raise GeneralError('No geometry views found.')
elif G.geometryviews:
tgeostart = perf_counter()
for geometryview in G.geometryviews:
geometryview.write_file(modelrun, numbermodelruns, G)
tgeoend = perf_counter()
print('\nGeometry file(s) written in [HH:MM:SS]: {}'.format(
datetime.timedelta(seconds=int(tgeoend - tgeostart))))
# Run simulation if not doing only geometry
if not args.geometry_only:
# Prepare any snapshot files
for snapshot in G.snapshots:
snapshot.prepare_file(modelrun, numbermodelruns, G)
# Prepare output file
inputfileparts = os.path.splitext(inputfile)
if numbermodelruns == 1:
outputfile = inputfileparts[0] + '.out'
else:
outputfile = inputfileparts[0] + str(modelrun) + '.out'
sys.stdout.write('\nOutput to file: {}\n'.format(outputfile))
sys.stdout.flush()
f = prepare_output_file(outputfile, G)
# Adjust position of sources and receivers if required
if G.srcstepx > 0 or G.srcstepy > 0 or G.srcstepz > 0:
for source in itertools.chain(G.hertziandipoles, G.magneticdipoles,
G.voltagesources,
G.transmissionlines):
source.xcoord += (modelrun - 1) * G.srcstepx
source.ycoord += (modelrun - 1) * G.srcstepy
source.zcoord += (modelrun - 1) * G.srcstepz
if G.rxstepx > 0 or G.rxstepy > 0 or G.rxstepz > 0:
for receiver in G.rxs:
receiver.xcoord += (modelrun - 1) * G.rxstepx
receiver.ycoord += (modelrun - 1) * G.rxstepy
receiver.zcoord += (modelrun - 1) * G.rxstepz
##################################
# Main FDTD calculation loop #
##################################
tsolvestart = perf_counter()
# Absolute time
abstime = 0
for timestep in range(G.iterations):
if timestep == 0:
tstepstart = perf_counter()
# Write field outputs to file
write_output(f, timestep, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz, G)
# Write any snapshots to file
for snapshot in G.snapshots:
if snapshot.time == timestep + 1:
snapshot.write_snapshot(G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz,
G)
# Update electric field components
if Material.maxpoles == 0: # All materials are non-dispersive so do standard update
update_electric(G.nx, G.ny, G.nz, G.nthreads, G.updatecoeffsE,
G.ID, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz)
elif Material.maxpoles == 1: # If there are any dispersive materials do 1st part of dispersive update (it is split into two parts as it requires present and updated electric field values).
update_electric_dispersive_1pole_A(G.nx, G.ny, G.nz,
G.nthreads, G.updatecoeffsE,
G.updatecoeffsdispersive,
G.ID, G.Tx, G.Ty, G.Tz,
G.Ex, G.Ey, G.Ez, G.Hx,
G.Hy, G.Hz)
elif Material.maxpoles > 1:
update_electric_dispersive_multipole_A(
G.nx, G.ny, G.nz, G.nthreads, Material.maxpoles,
G.updatecoeffsE, G.updatecoeffsdispersive, G.ID, G.Tx,
G.Ty, G.Tz, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz)
# Update electric field components with the PML correction
update_electric_pml(G)
# Update electric field components from sources
for voltagesource in G.voltagesources:
voltagesource.update_electric(abstime, G.updatecoeffsE, G.ID,
G.Ex, G.Ey, G.Ez, G)
for transmissionline in G.transmissionlines:
transmissionline.update_electric(abstime, G.Ex, G.Ey, G.Ez, G)
for hertziandipole in G.hertziandipoles: # Update any Hertzian dipole sources last
hertziandipole.update_electric(abstime, G.updatecoeffsE, G.ID,
G.Ex, G.Ey, G.Ez, G)
# If there are any dispersive materials do 2nd part of dispersive update (it is split into two parts as it requires present and updated electric field values). Therefore it can only be completely updated after the electric field has been updated by the PML and source updates.
if Material.maxpoles == 1:
update_electric_dispersive_1pole_B(G.nx, G.ny, G.nz,
G.nthreads,
G.updatecoeffsdispersive,
G.ID, G.Tx, G.Ty, G.Tz,
G.Ex, G.Ey, G.Ez)
elif Material.maxpoles > 1:
update_electric_dispersive_multipole_B(
G.nx, G.ny, G.nz, G.nthreads, Material.maxpoles,
G.updatecoeffsdispersive, G.ID, G.Tx, G.Ty, G.Tz, G.Ex,
G.Ey, G.Ez)
# Increment absolute time value
abstime += 0.5 * G.dt
# Update magnetic field components
update_magnetic(G.nx, G.ny, G.nz, G.nthreads, G.updatecoeffsH,
G.ID, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz)
# Update magnetic field components with the PML correction
update_magnetic_pml(G)
# Update magnetic field components from sources
for transmissionline in G.transmissionlines:
transmissionline.update_magnetic(abstime, G.Hx, G.Hy, G.Hz, G)
for magneticdipole in G.magneticdipoles:
magneticdipole.update_magnetic(abstime, G.updatecoeffsH, G.ID,
G.Hx, G.Hy, G.Hz, G)
# Increment absolute time value
abstime += 0.5 * G.dt
# Calculate time for two iterations, used to estimate overall runtime
if timestep == 1:
tstepend = perf_counter()
runtime = datetime.timedelta(
seconds=int((tstepend - tstepstart) / 2 * G.iterations))
sys.stdout.write(
'Estimated runtime [HH:MM:SS]: {}\n'.format(runtime))
sys.stdout.write('Solving for model run {} of {}...\n'.format(
modelrun, numbermodelruns))
sys.stdout.flush()
elif timestep > 1:
update_progress((timestep + 1) / G.iterations)
# Close output file
f.close()
tsolveend = perf_counter()
print('\n\nSolving took [HH:MM:SS]: {}'.format(
datetime.timedelta(seconds=int(tsolveend - tsolvestart))))
print('Peak memory (approx) used: {}'.format(
human_size(p.memory_info().rss)))
def run_model(args, currentmodelrun, numbermodelruns, inputfile,
usernamespace):
"""Runs a model - processes the input file; builds the Yee cells; calculates update coefficients; runs main FDTD loop.
Args:
args (dict): Namespace with command line arguments
currentmodelrun (int): Current model run number.
numbermodelruns (int): Total number of model runs.
inputfile (object): File object for the input file.
usernamespace (dict): Namespace that can be accessed by user in any Python code blocks in input file.
Returns:
tsolve (int): Length of time (seconds) of main FDTD calculations
"""
# Monitor memory usage
p = psutil.Process()
# Declare variable to hold FDTDGrid class
global G
# Normal model reading/building process; bypassed if geometry information to be reused
if 'G' not in globals():
# Initialise an instance of the FDTDGrid class
G = FDTDGrid()
G.inputfilename = os.path.split(inputfile.name)[1]
G.inputdirectory = os.path.dirname(os.path.abspath(inputfile.name))
inputfilestr = '\n--- Model {}/{}, input file: {}'.format(
currentmodelrun, numbermodelruns, inputfile.name)
print(Fore.GREEN + '{} {}\n'.format(
inputfilestr, '-' *
(get_terminal_width() - 1 - len(inputfilestr))) + Style.RESET_ALL)
# Add the current model run to namespace that can be accessed by user in any Python code blocks in input file
usernamespace['current_model_run'] = currentmodelrun
# Read input file and process any Python or include commands
processedlines = process_python_include_code(inputfile, usernamespace)
# Print constants/variables in user-accessable namespace
uservars = ''
for key, value in sorted(usernamespace.items()):
if key != '__builtins__':
uservars += '{}: {}, '.format(key, value)
print(
'Constants/variables used/available for Python scripting: {{{}}}\n'
.format(uservars[:-2]))
# Write a file containing the input commands after Python or include commands have been processed
if args.write_processed:
write_processed_file(
os.path.join(G.inputdirectory, G.inputfilename),
currentmodelrun, numbermodelruns, processedlines)
# Check validity of command names and that essential commands are present
singlecmds, multicmds, geometry = check_cmd_names(processedlines)
# Create built-in materials
m = Material(0, 'pec')
m.se = float('inf')
m.type = 'builtin'
m.averagable = False
G.materials.append(m)
m = Material(1, 'free_space')
m.type = 'builtin'
G.materials.append(m)
# Process parameters for commands that can only occur once in the model
process_singlecmds(singlecmds, G)
# Process parameters for commands that can occur multiple times in the model
print()
process_multicmds(multicmds, G)
# Initialise an array for volumetric material IDs (solid), boolean arrays for specifying materials not to be averaged (rigid),
# an array for cell edge IDs (ID)
G.initialise_geometry_arrays()
# Initialise arrays for the field components
G.initialise_field_arrays()
# Process geometry commands in the order they were given
process_geometrycmds(geometry, G)
# Build the PMLs and calculate initial coefficients
print()
if all(value == 0 for value in G.pmlthickness.values()):
if G.messages:
print('PML boundaries: switched off')
pass # If all the PMLs are switched off don't need to build anything
else:
if G.messages:
if all(value == G.pmlthickness['x0']
for value in G.pmlthickness.values()):
pmlinfo = str(G.pmlthickness['x0']) + ' cells'
else:
pmlinfo = ''
for key, value in G.pmlthickness.items():
pmlinfo += '{}: {} cells, '.format(key, value)
pmlinfo = pmlinfo[:-2]
print('PML boundaries: {}'.format(pmlinfo))
pbar = tqdm(total=sum(1 for value in G.pmlthickness.values()
if value > 0),
desc='Building PML boundaries',
ncols=get_terminal_width() - 1,
file=sys.stdout,
disable=G.tqdmdisable)
build_pmls(G, pbar)
pbar.close()
# Build the model, i.e. set the material properties (ID) for every edge of every Yee cell
print()
pbar = tqdm(total=2,
desc='Building main grid',
ncols=get_terminal_width() - 1,
file=sys.stdout,
disable=G.tqdmdisable)
build_electric_components(G.solid, G.rigidE, G.ID, G)
pbar.update()
build_magnetic_components(G.solid, G.rigidH, G.ID, G)
pbar.update()
pbar.close()
# Process any voltage sources (that have resistance) to create a new material at the source location
for voltagesource in G.voltagesources:
voltagesource.create_material(G)
# Initialise arrays of update coefficients to pass to update functions
G.initialise_std_update_coeff_arrays()
# Initialise arrays of update coefficients and temporary values if there are any dispersive materials
if Material.maxpoles != 0:
G.initialise_dispersive_arrays()
# Process complete list of materials - calculate update coefficients, store in arrays, and build text list of materials/properties
materialsdata = process_materials(G)
if G.messages:
materialstable = AsciiTable(materialsdata)
materialstable.outer_border = False
materialstable.justify_columns[0] = 'right'
print(materialstable.table)
# Check to see if numerical dispersion might be a problem
results = dispersion_analysis(G)
if not results['waveform']:
print(
Fore.RED +
"\nWARNING: Numerical dispersion analysis not carried out as either no waveform detected or waveform does not fit within specified time window and is therefore being truncated."
+ Style.RESET_ALL)
elif results['N'] < G.mingridsampling:
raise GeneralError(
"Non-physical wave propagation: Material '{}' has wavelength sampled by {} cells, less than required minimum for physical wave propagation. Maximum significant frequency estimated as {:g}Hz"
.format(results['material'].ID, results['N'],
results['maxfreq']))
elif results['deltavp'] and np.abs(
results['deltavp']) > G.maxnumericaldisp:
print(
Fore.RED +
"\nWARNING: Potentially significant numerical dispersion. Estimated largest physical phase-velocity error is {:.2f}% in material '{}' whose wavelength sampled by {} cells. Maximum significant frequency estimated as {:g}Hz"
.format(results['deltavp'], results['material'].ID,
results['N'], results['maxfreq']) + Style.RESET_ALL)
elif results['deltavp'] and G.messages:
print(
"\nNumerical dispersion analysis: estimated largest physical phase-velocity error is {:.2f}% in material '{}' whose wavelength sampled by {} cells. Maximum significant frequency estimated as {:g}Hz"
.format(results['deltavp'], results['material'].ID,
results['N'], results['maxfreq']))
# If geometry information to be reused between model runs
else:
inputfilestr = '\n--- Model {}/{}, input file (not re-processed, i.e. geometry fixed): {}'.format(
currentmodelrun, numbermodelruns, inputfile.name)
print(Fore.GREEN + '{} {}\n'.format(
inputfilestr, '-' *
(get_terminal_width() - 1 - len(inputfilestr))) + Style.RESET_ALL)
# Clear arrays for field components
G.initialise_field_arrays()
# Clear arrays for fields in PML
for pml in G.pmls:
pml.initialise_field_arrays()
# Adjust position of simple sources and receivers if required
if G.srcsteps[0] != 0 or G.srcsteps[1] != 0 or G.srcsteps[2] != 0:
for source in itertools.chain(G.hertziandipoles, G.magneticdipoles):
if currentmodelrun == 1:
if source.xcoord + G.srcsteps[0] * (
numbermodelruns -
1) < 0 or source.xcoord + G.srcsteps[0] * (
numbermodelruns -
1) > G.nx or source.ycoord + G.srcsteps[1] * (
numbermodelruns -
1) < 0 or source.ycoord + G.srcsteps[1] * (
numbermodelruns - 1
) > G.ny or source.zcoord + G.srcsteps[2] * (
numbermodelruns -
1) < 0 or source.zcoord + G.srcsteps[2] * (
numbermodelruns - 1) > G.nz:
raise GeneralError(
'Source(s) will be stepped to a position outside the domain.'
)
source.xcoord = source.xcoordorigin + (currentmodelrun -
1) * G.srcsteps[0]
source.ycoord = source.ycoordorigin + (currentmodelrun -
1) * G.srcsteps[1]
source.zcoord = source.zcoordorigin + (currentmodelrun -
1) * G.srcsteps[2]
if G.rxsteps[0] != 0 or G.rxsteps[1] != 0 or G.rxsteps[2] != 0:
for receiver in G.rxs:
if currentmodelrun == 1:
if receiver.xcoord + G.rxsteps[0] * (
numbermodelruns -
1) < 0 or receiver.xcoord + G.rxsteps[0] * (
numbermodelruns -
1) > G.nx or receiver.ycoord + G.rxsteps[1] * (
numbermodelruns -
1) < 0 or receiver.ycoord + G.rxsteps[1] * (
numbermodelruns - 1
) > G.ny or receiver.zcoord + G.rxsteps[2] * (
numbermodelruns - 1
) < 0 or receiver.zcoord + G.rxsteps[2] * (
numbermodelruns - 1) > G.nz:
raise GeneralError(
'Receiver(s) will be stepped to a position outside the domain.'
)
receiver.xcoord = receiver.xcoordorigin + (currentmodelrun -
1) * G.rxsteps[0]
receiver.ycoord = receiver.ycoordorigin + (currentmodelrun -
1) * G.rxsteps[1]
receiver.zcoord = receiver.zcoordorigin + (currentmodelrun -
1) * G.rxsteps[2]
# Write files for any geometry views and geometry object outputs
if not (G.geometryviews or G.geometryobjectswrite) and args.geometry_only:
print(
Fore.RED +
'\nWARNING: No geometry views or geometry objects to output found.'
+ Style.RESET_ALL)
if G.geometryviews:
print()
for i, geometryview in enumerate(G.geometryviews):
geometryview.set_filename(currentmodelrun, numbermodelruns, G)
pbar = tqdm(total=geometryview.datawritesize,
unit='byte',
unit_scale=True,
desc='Writing geometry view file {}/{}, {}'.format(
i + 1, len(G.geometryviews),
os.path.split(geometryview.filename)[1]),
ncols=get_terminal_width() - 1,
file=sys.stdout,
disable=G.tqdmdisable)
geometryview.write_vtk(currentmodelrun, numbermodelruns, G, pbar)
pbar.close()
if G.geometryobjectswrite:
for i, geometryobject in enumerate(G.geometryobjectswrite):
pbar = tqdm(total=geometryobject.datawritesize,
unit='byte',
unit_scale=True,
desc='Writing geometry object file {}/{}, {}'.format(
i + 1, len(G.geometryobjectswrite),
os.path.split(geometryobject.filename)[1]),
ncols=get_terminal_width() - 1,
file=sys.stdout,
disable=G.tqdmdisable)
geometryobject.write_hdf5(G, pbar)
pbar.close()
# Run simulation (if not only looking ar geometry information)
if not args.geometry_only:
# Prepare any snapshot files
for snapshot in G.snapshots:
snapshot.prepare_vtk_imagedata(currentmodelrun, numbermodelruns, G)
# Output filename
inputfileparts = os.path.splitext(
os.path.join(G.inputdirectory, G.inputfilename))
if numbermodelruns == 1:
outputfile = inputfileparts[0] + '.out'
else:
outputfile = inputfileparts[0] + str(currentmodelrun) + '.out'
print('\nOutput file: {}\n'.format(outputfile))
# Main FDTD solving functions for either CPU or GPU
tsolve = solve_cpu(currentmodelrun, numbermodelruns, G)
# Write an output file in HDF5 format
write_hdf5_outputfile(outputfile, G.Ex, G.Ey, G.Ez, G.Hx, G.Hy, G.Hz,
G)
if G.messages:
print('Memory (RAM) used: ~{}'.format(
human_size(p.memory_info().rss)))
print('Solving time [HH:MM:SS]: {}'.format(
datetime.timedelta(seconds=tsolve)))
return tsolve
# If geometry information to be reused between model runs then FDTDGrid class instance must be global so that it persists
if not args.geometry_fixed:
del G
import os, struct, argparse
import numpy as np
from gprMax.grid import FDTDGrid
from gprMax.receivers import Rx
from gprMax.fields_output import prepare_output_file, write_output
"""Converts old output file to new HDF5 format."""
# Parse command line arguments
parser = argparse.ArgumentParser(description='Converts old output file to new HDF5 format.', usage='cd gprMax; python -m tools.outputfile_old2hdf5 outputfile')
parser.add_argument('outputfile', help='name of output file including path')
args = parser.parse_args()
outputfile = args.outputfile
G = FDTDGrid()
print("Reading: '{}'".format(outputfile))
with open(outputfile, 'rb') as f:
# Get information from file header
f.read(2)
filetype, = struct.unpack('h', f.read(2))
myshort, = struct.unpack('h', f.read(2))
myfloat, = struct.unpack('h', f.read(2))
titlelength, = struct.unpack('h', f.read(2))
sourcelength, = struct.unpack('h', f.read(2))
medialength, = struct.unpack('h', f.read(2))
reserved, = struct.unpack('h', f.read(2))
G.title = ''
for c in range(titlelength):
