def create_tablewriter(self):
entities_energy = {
"step": {"unit": "<1>", "get": lambda sim: sim.step, "header": "steps"},
"energy": {
"unit": "<J>",
"get": lambda sim: sim.energy,
"header": ["image_%d" % i for i in range(self.image_num + 2)],
},
}
self.tablewriter = DataSaver(self, "%s_energy.ndt" % (self.name), entities=entities_energy)
entities_dm = {
"step": {"unit": "<1>", "get": lambda sim: sim.step, "header": "steps"},
"dms": {
"unit": "<1>",
"get": lambda sim: sim.distances,
"header": ["image_%d_%d" % (i, i + 1) for i in range(self.image_num + 1)],
},
}
self.tablewriter_dm = DataSaver(self, "%s_dms.ndt" % (self.name), entities=entities_dm)
def create_tablewriter(self):
entities_energy = {
'step': {
'unit': '<1>',
'get': lambda sim: sim.step,
'header': 'steps'
},
'energy': {
'unit': '<J>',
'get': lambda sim: sim.energy,
'header': ['image_%d' % i for i in range(self.image_num + 2)]
}
}
self.tablewriter = DataSaver(self,
'%s_energy.ndt' % (self.name),
entities=entities_energy)
entities_dm = {
'step': {
'unit': '<1>',
'get': lambda sim: sim.step,
'header': 'steps'
},
'dms': {
'unit':
'<1>',
'get':
lambda sim: sim.distances,
'header': [
'image_%d_%d' % (i, i + 1)
for i in range(self.image_num + 1)
]
}
}
self.tablewriter_dm = DataSaver(self,
'%s_dms.ndt' % (self.name),
entities=entities_dm)
def create_tablewriter(self):
entities_energy = {
'step': {'unit': '<1>',
'get': lambda sim: sim.step,
'header': 'steps'},
'energy': {'unit': '<J>',
'get': lambda sim: sim.energy,
'header': ['image_%d' % i for i in range(self.image_num + 2)]}
}
self.tablewriter = DataSaver(
self, '%s_energy.ndt' % (self.name), entities=entities_energy)
entities_dm = {
'step': {'unit': '<1>',
'get': lambda sim: sim.step,
'header': 'steps'},
'dms': {'unit': '<1>',
'get': lambda sim: sim.distances,
'header': ['image_%d_%d' % (i, i + 1) for i in range(self.image_num + 1)]}
}
self.tablewriter_dm = DataSaver(
self, '%s_dms.ndt' % (self.name), entities=entities_dm)
class NEB_Sundials(object):
"""
Nudged elastic band method by solving the differential equation using Sundials.
"""
def __init__(self, sim, initial_images, climbing_image=None, interpolations=None, spring=5e5, name="unnamed"):
"""
*Arguments*
sim: the Simulation class
initial_images: a list contain the initial value, which can have
any of the forms accepted by the function 'finmag.util.helpers.
vector_valued_function', for example,
initial_images = [(0,0,1), (0,0,-1)]
or with given defined function
def init_m(pos):
x=pos[0]
if x<10:
return (0,1,1)
return (-1,0,0)
initial_images = [(0,0,1), (0,0,-1), init_m ]
are accepted forms.
climbing_image : An integer with the index (from 1 to the total
number of images minus two; it doesn't have any sense to use the
extreme images) of the image with the largest energy, which will
be updated in the NEB algorithm using the Climbing Image NEB
method (no spring force and "with the component along the elastic
band inverted" [*]). See: [*] Henkelman et al., The Journal of
Chemical Physics 113, 9901 (2000)
interpolations : a list only contain integers and the length of
this list should equal to the length of the initial_images minus
1, i.e., len(interpolations) = len(initial_images) - 1 ** THIS IS
not well defined in CARTESIAN coordinates**
spring: the spring constant, a float value
disable_tangent: this is an experimental option, by disabling the
tangent, we can get a rough feeling about the local energy minima
quickly.
"""
self.sim = sim
self.name = name
self.spring = spring
# We set a minus one because the *sundials_rhs* function
# only uses an array without counting the extreme images,
# whose length is self.image_num (see below)
if climbing_image is not None:
self.climbing_image = climbing_image - 1
else:
self.climbing_image = climbing_image
if interpolations is None:
interpolations = [0 for i in range(len(initial_images) - 1)]
self.initial_images = initial_images
self.interpolations = interpolations
if len(interpolations) != len(initial_images) - 1:
raise RuntimeError(
"""The length of interpolations should be equal to
the length of the initial_images array minus 1, i.e.,
len(interpolations) = len(initial_images) - 1"""
)
if len(initial_images) < 2:
raise RuntimeError(
"""At least two images must be provided
to create the energy band"""
)
# the total image number including two ends
self.total_image_num = len(initial_images) + sum(interpolations)
self.image_num = self.total_image_num - 2
self.n = sim.n
self.coords = np.zeros(3 * self.n * self.total_image_num)
self.last_m = np.zeros(self.coords.shape)
self.Heff = np.zeros(self.coords.shape)
self.Heff.shape = (self.total_image_num, -1)
self.tangents = np.zeros(3 * self.n * self.image_num)
self.tangents.shape = (self.image_num, -1)
self.energy = np.zeros(self.total_image_num)
self.springs = np.zeros(self.image_num)
self.pin_ids = np.array([i for i, v in enumerate(self.sim.pins) if v > 0], dtype=np.int32)
self.t = 0
self.step = 0
self.ode_count = 1
self.integrator = None
self.initial_image_coordinates()
self.create_tablewriter()
def create_tablewriter(self):
entities_energy = {
"step": {"unit": "<1>", "get": lambda sim: sim.step, "header": "steps"},
"energy": {
"unit": "<J>",
"get": lambda sim: sim.energy,
"header": ["image_%d" % i for i in range(self.image_num + 2)],
},
}
self.tablewriter = DataSaver(self, "%s_energy.ndt" % (self.name), entities=entities_energy)
entities_dm = {
"step": {"unit": "<1>", "get": lambda sim: sim.step, "header": "steps"},
"dms": {
"unit": "<1>",
"get": lambda sim: sim.distances,
"header": ["image_%d_%d" % (i, i + 1) for i in range(self.image_num + 1)],
},
}
self.tablewriter_dm = DataSaver(self, "%s_dms.ndt" % (self.name), entities=entities_dm)
def initial_image_coordinates(self):
"""
Generate the coordinates linearly according to the number of
interpolations provided.
Example: Imagine we have 4 images and we want 3 interpolations
between every neighbouring pair, i.e interpolations = [3, 3, 3]
1. Imagine the initial states with the interpolation numbers
and choose the first and second state
0 1 2 3
X -------- X --------- X -------- X
3 3 3
2. Counter image_id is set to 0
3. Set the image 0 magnetisation vector as m0 and append the
values to self.coords[0]. Update the counter: image_id = 1 now
4. Set the image 1 magnetisation values as m1 and interpolate
the values between m0 and m1, generating 3 arrays
with the magnetisation values of every interpolation image.
For every array, append the values to self.coords[i]
with i = 1, 2 and 3 ; updating the counter every time, so
image_id = 4 now
5. Append the value of m1 (image 1) in self.coords[4]
Update counter (image_id = 5 now)
6. Move to the next pair of images, now set the 1-th image
magnetisation values as m0 and append to self.coords[5]
7. Interpolate to get self.coords[i], for i = 6, 7, 8
...
8. Repeat as before until move to the pair of images: 2 - 3
9. Finally append the magnetisation of the last image
(self.initial_images[-1]). In this case, the 3rd image
Then, for every magnetisation vector values array (self.coords[i])
append the value to the simulation and store the energies
corresponding to every i-th image to the self.energy[i] arrays
Finally, flatten the self.coords matrix (containing the magnetisation
values of every image in different rows)
** Our generalised coordinates in the NEBM are the magnetisation values
"""
# Initiate the counter
image_id = 0
self.coords.shape = (self.total_image_num, -1)
# For every interpolation between images (zero if no interpolations
# were specified)
for i in range(len(self.interpolations)):
# Store the number
n = self.interpolations[i]
# Save on the first image of a pair (step 1, 6, ...)
self.sim.set_m(self.initial_images[i])
m0 = self.sim.spin.copy()
self.coords[image_id][:] = m0[:]
image_id = image_id + 1
# Set the second image in the pair as m1 and interpolate
# (step 4 and 7), saving in corresponding self.coords entries
self.sim.set_m(self.initial_images[i + 1])
m1 = self.sim.spin.copy()
# Interpolations (arrays with magnetisation values)
coords = linear_interpolation_two(m0, m1, n, self.pin_ids)
for coord in coords:
self.coords[image_id][:] = coord[:]
image_id = image_id + 1
# Continue to the next pair of images
# Append the magnetisation of the last image
self.sim.set_m(self.initial_images[-1])
m2 = self.sim.spin
self.coords[image_id][:] = m2[:]
# Save the energies
for i in range(self.total_image_num):
self.sim.spin[:] = self.coords[i][:]
self.sim.compute_effective_field(t=0)
self.energy[i] = self.sim.compute_energy()
# Flatten the array
self.coords.shape = (-1,)
def add_noise(self, T=0.1):
noise = T * np.random.rand(self.total_image_num, 3, self.n)
noise[:, :, self.pin_ids] = 0
noise[0, :, :] = 0
noise[-1, :, :] = 0
noise.shape = (-1,)
self.coords += noise
def save_vtks(self):
"""
Save vtk files in different folders, according to the
simulation name and step.
Files are saved as vtks/simname_simstep_vtk/image_00000x.vtk
"""
# Create the directory
directory = "vtks/%s_%d" % (self.name, self.step)
self.vtk = SaveVTK(self.sim.mesh, directory)
self.coords.shape = (self.total_image_num, -1)
# We use Ms from the simulation assuming that all the
# images are the same
for i in range(self.total_image_num):
# We will try to save for the micromagnetic simulation (Ms)
# or an atomistic simulation (mu_s)
# TODO: maybe this can be done with an: isinstance
try:
self.vtk.save_vtk(self.coords[i].reshape(-1, 3), self.sim.Ms, step=i, vtkname="m")
except:
self.vtk.save_vtk(self.coords[i].reshape(-1, 3), self.sim._mu_s, step=i, vtkname="m")
self.coords.shape = (-1,)
def save_npys(self):
"""
Save npy files in different folders according to
the simulation name and step
Files are saved as: npys/simname_simstep/image_x.npy
"""
# Create directory as simname_simstep
directory = "npys/%s_%d" % (self.name, self.step)
if not os.path.exists(directory):
os.makedirs(directory)
# Save the images with the format: 'image_{}.npy'
# where {} is the image number, starting from 0
self.coords.shape = (self.total_image_num, -1)
for i in range(self.total_image_num):
name = os.path.join(directory, "image_%d.npy" % i)
np.save(name, self.coords[i, :])
self.coords.shape = (-1,)
def create_integrator(self, rtol=1e-6, atol=1e-6, nsteps=10000):
self.integrator = cvode.CvodeSolver(self.coords, self.sundials_rhs)
self.integrator.set_options(rtol, atol)
def compute_effective_field(self, y):
y.shape = (self.total_image_num, -1)
for i in range(self.image_num):
self.sim.spin[:] = y[i + 1][:]
#
self.sim.compute_effective_field(t=0)
# Compute effective field, which is the gradient of
# the energy in the NEB method (derivative with respect to
# the generalised coordinates)
h = self.sim.field
#
self.Heff[i + 1, :] = h[:]
# Compute the total energy
self.energy[i + 1] = self.sim.compute_energy()
# Compute the 'distance' or difference between neighbouring states
# around y[i+1]. This is used to compute the spring force
#
dm1 = compute_dm(y[i], y[i + 1])
dm2 = compute_dm(y[i + 1], y[i + 2])
self.springs[i] = self.spring * (dm2 - dm1)
# Use the native NEB (C code) to compute the tangents according
# to the improved NEB method, developed by Henkelman and Jonsson
# at: Henkelman et al., Journal of Chemical Physics 113, 22 (2000)
neb_clib.compute_tangents(y, self.energy, self.tangents, self.total_image_num, 3 * self.n)
# native_neb.compute_springs(y,self.springs,self.spring)
y.shape = (-1,)
def sundials_rhs(self, time, y, ydot):
"""
Right hand side of the optimization scheme used to find the minimum
energy path. In our case, we use a LLG kind of equation:
d Y / dt = Y x Y x D
D = -( nabla E + [nabla E * t] t ) + F_spring
where Y is an image: Y = (M_0, ... , M_N) and t is the tangent vector
defined according to the energy of the neighbouring images (see
Henkelman et al publication)
If a climbing_image index is specified, the corresponding image
will be iterated without the spring force and with an inversed
component along the tangent
"""
# Update the ODE solver
self.ode_count += 1
# Compute the eff field H for every image, H = -nabla E
# (derived with respect to M)
self.compute_effective_field(y)
# Reshape y and ydot in a matrix of total_image_num rows
y.shape = (self.total_image_num, -1)
ydot.shape = (self.total_image_num, -1)
# Compute the total force for every image (not the extremes)
# Rememeber that self.image_num = self.total_image_num - 2
# The total force is:
# D = - (-nabla E + [nabla E * t] t) + F_spring
# This value is different is a climbing image is specified:
# D_climb = -nabla E + 2 * [nabla E * t] t
for i in range(self.image_num):
h = self.Heff[i + 1]
t = self.tangents[i]
sf = self.springs[i]
if not (self.climbing_image and i == self.climbing_image):
h3 = h - np.dot(h, t) * t + sf * t
else:
h3 = h - 2 * np.dot(h, t) * t
# Update H_eff[i + 1] with the new h3
h[:] = h3[:]
# Update the step with the optimisation algorithm, in this
# case we use: dY /dt = Y x Y x D
# (check the C code in common/)
neb_clib.compute_dm_dt(y, self.Heff, ydot, self.sim._pins, self.total_image_num, self.n)
ydot[0, :] = 0
ydot[-1, :] = 0
y.shape = (-1,)
ydot.shape = (-1,)
return 0
def compute_distance(self):
distance = []
ys = self.coords
ys.shape = (self.total_image_num, -1)
for i in range(self.total_image_num - 1):
dm = compute_dm(ys[i], ys[i + 1])
distance.append(dm)
ys.shape = (-1,)
self.distances = np.array(distance)
def run_until(self, t):
if t <= self.t:
return
self.integrator.run_until(t)
self.coords[:] = self.integrator.y[:]
m = self.coords
y = self.last_m
m.shape = (self.total_image_num, -1)
y.shape = (self.total_image_num, -1)
max_dmdt = 0
for i in range(1, self.image_num + 1):
dmdt = compute_dm(y[i], m[i]) / (t - self.t)
if dmdt > max_dmdt:
max_dmdt = dmdt
m.shape = (-1,)
y.shape = (-1,)
self.last_m[:] = m[:]
self.t = t
return max_dmdt
def relax(self, dt=1e-8, stopping_dmdt=1e4, max_steps=1000, save_npy_steps=100, save_vtk_steps=100):
if self.integrator is None:
self.create_integrator()
log.debug(
"Relaxation parameters: "
"stopping_dmdt={} (degrees per nanosecond), "
"time_step={} s, max_steps={}.".format(stopping_dmdt, dt, max_steps)
)
# Save the initial state i=0
self.compute_distance()
self.tablewriter.save()
self.tablewriter_dm.save()
for i in range(max_steps):
if i % save_vtk_steps == 0:
self.save_vtks()
if i % save_npy_steps == 0:
self.save_npys()
self.step += 1
cvode_dt = self.integrator.get_current_step()
increment_dt = dt
if cvode_dt > dt:
increment_dt = cvode_dt
dmdt = self.run_until(self.t + increment_dt)
self.compute_distance()
self.tablewriter.save()
self.tablewriter_dm.save()
log.debug("step: {:.3g}, step_size: {:.3g}" " and max_dmdt: {:.3g}.".format(self.step, increment_dt, dmdt))
if dmdt < stopping_dmdt:
break
log.info(
"Relaxation finished at time step = {:.4g}, "
"t = {:.2g}, call rhs = {:.4g} "
"and max_dmdt = {:.3g}".format(self.step, self.t, self.ode_count, dmdt)
)
self.save_vtks()
self.save_npys()
class NEB_Sundials(object):
"""
Nudged elastic band method by solving the differential equation using Sundials.
"""
def __init__(self,
sim,
initial_images,
climbing_image=None,
interpolations=None,
spring=5e5,
name='unnamed'):
"""
*Arguments*
sim: the Simulation class
initial_images: a list contain the initial value, which can have
any of the forms accepted by the function 'finmag.util.helpers.
vector_valued_function', for example,
initial_images = [(0,0,1), (0,0,-1)]
or with given defined function
def init_m(pos):
x=pos[0]
if x<10:
return (0,1,1)
return (-1,0,0)
initial_images = [(0,0,1), (0,0,-1), init_m ]
are accepted forms.
climbing_image : An integer with the index (from 1 to the total
number of images minus two; it doesn't have any sense to use the
extreme images) of the image with the largest energy, which will
be updated in the NEB algorithm using the Climbing Image NEB
method (no spring force and "with the component along the elastic
band inverted" [*]). See: [*] Henkelman et al., The Journal of
Chemical Physics 113, 9901 (2000)
interpolations : a list only contain integers and the length of
this list should equal to the length of the initial_images minus
1, i.e., len(interpolations) = len(initial_images) - 1 ** THIS IS
not well defined in CARTESIAN coordinates**
spring: the spring constant, a float value
disable_tangent: this is an experimental option, by disabling the
tangent, we can get a rough feeling about the local energy minima
quickly.
"""
self.sim = sim
self.name = name
self.spring = spring
# We set a minus one because the *sundials_rhs* function
# only uses an array without counting the extreme images,
# whose length is self.image_num (see below)
if climbing_image is not None:
self.climbing_image = climbing_image - 1
else:
self.climbing_image = climbing_image
if interpolations is None:
interpolations = [0 for i in range(len(initial_images) - 1)]
self.initial_images = initial_images
self.interpolations = interpolations
if len(interpolations) != len(initial_images) - 1:
raise RuntimeError(
"""The length of interpolations should be equal to
the length of the initial_images array minus 1, i.e.,
len(interpolations) = len(initial_images) - 1""")
if len(initial_images) < 2:
raise RuntimeError("""At least two images must be provided
to create the energy band""")
# the total image number including two ends
self.total_image_num = len(initial_images) + sum(interpolations)
self.image_num = self.total_image_num - 2
# Number of nodes (spins)
self.n = sim.n
# Total number of spherical coordinates
# (2 components per spin for every image)
self.coords = np.zeros(2 * self.n * self.total_image_num)
self.last_m = np.zeros(self.coords.shape)
# For the effective field we use the extremes (to fit the energies
# array length). We could save some memory if we don't consider them
# (CHECK this in the future)
self.Heff = np.zeros(self.coords.shape)
# self.Heff = np.zeros(2 * self.n * self.total_image_num)
self.Heff.shape = (self.total_image_num, -1)
# Tangent components in spherical coordinates
self.tangents = np.zeros(2 * self.n * self.image_num)
self.tangents.shape = (self.image_num, -1)
self.energy = np.zeros(self.total_image_num)
self.springs = np.zeros(self.image_num)
self.pin_ids = np.array(
[i for i, v in enumerate(self.sim.pins) if v > 0], dtype=np.int32)
self.t = 0
self.step = 0
self.ode_count = 1
self.integrator = None
self.initial_image_coordinates()
self.create_tablewriter()
def create_tablewriter(self):
entities_energy = {
'step': {
'unit': '<1>',
'get': lambda sim: sim.step,
'header': 'steps'
},
'energy': {
'unit': '<J>',
'get': lambda sim: sim.energy,
'header': ['image_%d' % i for i in range(self.image_num + 2)]
}
}
self.tablewriter = DataSaver(self,
'%s_energy.ndt' % (self.name),
entities=entities_energy)
entities_dm = {
'step': {
'unit': '<1>',
'get': lambda sim: sim.step,
'header': 'steps'
},
'dms': {
'unit':
'<1>',
'get':
lambda sim: sim.distances,
'header': [
'image_%d_%d' % (i, i + 1)
for i in range(self.image_num + 1)
]
}
}
self.tablewriter_dm = DataSaver(self,
'%s_dms.ndt' % (self.name),
entities=entities_dm)
def initial_image_coordinates(self):
"""
Generate the coordinates linearly according to the number of
interpolations provided.
Example: Imagine we have 4 images and we want 3 interpolations
between every neighbouring pair, i.e interpolations = [3, 3, 3]
1. Imagine the initial states with the interpolation numbers
and choose the first and second state
0 1 2 3
X -------- X --------- X -------- X
3 3 3
2. Counter image_id is set to 0
3. Set the image 0 magnetisation vector as m0 and append the
values to self.coords[0]. Update the counter: image_id = 1 now
4. Set the image 1 magnetisation values as m1 and interpolate
the values between m0 and m1, generating 3 arrays
with the magnetisation values of every interpolation image.
For every array, append the values to self.coords[i]
with i = 1, 2 and 3 ; updating the counter every time, so
image_id = 4 now
5. Append the value of m1 (image 1) in self.coords[4]
Update counter (image_id = 5 now)
6. Move to the next pair of images, now set the 1-th image
magnetisation values as m0 and append to self.coords[5]
7. Interpolate to get self.coords[i], for i = 6, 7, 8
...
8. Repeat as before until move to the pair of images: 2 - 3
9. Finally append the magnetisation of the last image
(self.initial_images[-1]). In this case, the 3rd image
Then, for every magnetisation vector values array (self.coords[i])
append the value to the simulation and store the energies
corresponding to every i-th image to the self.energy[i] arrays
Finally, flatten the self.coords matrix (containing the magnetisation
values of every image in different rows)
** Our generalised coordinates in the NEBM are the magnetisation values
*** Remember that the sim.spin object has the spins as:
[mx1, my1, mz1, mx2, my2, ... ]
and we transform to spherical coordinates as
[theta1, phi1, theta2, phi2, ... ]
Thus if we have N + 1 images and P + 1 spins, and naming
the i-th image coordinates as thetai_j, phii_j,
for the j-th spin, then the flattened array at the end is:
[theta0_0, phi0_0, theta0_1, phi0_1, ... ,
theta0_P, phi0_P, theta1_0, phi1_0, ...,
thetaN_0, phiN_0, ..., thetaN_P, phiN_P]
"""
# Initiate the counter
image_id = 0
self.coords.shape = (self.total_image_num, -1)
# For every interpolation between images (zero if no interpolations
# were specified)
for i in range(len(self.interpolations)):
# Store the number
n = self.interpolations[i]
# Save on the first image of a pair (step 1, 6, ...)
self.sim.set_m(self.initial_images[i])
m0 = self.sim.spin.copy()
# Save the spin components in spherical coordinates
self.coords[image_id][:] = cartesian2spherical(m0[:])
image_id = image_id + 1
# Set the second image in the pair as m1 and interpolate
# (step 4 and 7), saving in corresponding self.coords entries
self.sim.set_m(self.initial_images[i + 1])
m1 = self.sim.spin.copy()
# Interpolations (arrays with magnetisation values)
coords = linear_interpolation_two(m0, m1, n, self.pin_ids)
for coord in coords:
self.coords[image_id][:] = coord[:]
image_id = image_id + 1
# Continue to the next pair of images
# Append the magnetisation of the last image in spherical coords
self.sim.set_m(self.initial_images[-1])
m2 = self.sim.spin
self.coords[image_id][:] = cartesian2spherical(m2[:])
# Save the energies
for i in range(self.total_image_num):
self.sim.spin[:] = spherical2cartesian(self.coords[i][:])
self.sim.compute_effective_field(t=0)
self.energy[i] = self.sim.compute_energy()
# Flatten the array
self.coords.shape = (-1, )
def add_noise(self, T=0.1):
noise = T * np.random.rand(self.total_image_num, 3, self.n)
noise[:, :, self.pin_ids] = 0
noise[0, :, :] = 0
noise[-1, :, :] = 0
noise.shape = (-1, )
self.coords += noise
def save_vtks(self):
"""
Save vtk files in different folders, according to the
simulation name and step.
Files are saved as vtks/simname_simstep_vtk/image_00000x.vtk
"""
# Create the directory
directory = 'vtks/%s_%d' % (self.name, self.step)
self.vtk = SaveVTK(self.sim.mesh, directory)
self.coords.shape = (self.total_image_num, -1)
for i in range(self.total_image_num):
self.vtk.save_vtk(spherical2cartesian(self.coords[i]),
step=i,
vtkname='m')
self.coords.shape = (-1, )
def save_npys(self):
"""
Save npy files in different folders according to
the simulation name and step
Files are saved as: npys/simname_simstep/image_x.npy
"""
# Create directory as simname_simstep
directory = 'npys/%s_%d' % (self.name, self.step)
if not os.path.exists(directory):
os.makedirs(directory)
# Save the images with the format: 'image_{}.npy'
# where {} is the image number, starting from 0
self.coords.shape = (self.total_image_num, -1)
for i in range(self.total_image_num):
name = os.path.join(directory, 'image_%d.npy' % i)
np.save(name, spherical2cartesian(self.coords[i, :]))
self.coords.shape = (-1, )
def create_integrator(self, rtol=1e-6, atol=1e-6, nsteps=10000):
self.integrator = cvode.CvodeSolver(self.coords, self.sundials_rhs)
self.integrator.set_options(rtol, atol)
def compute_effective_field(self, y):
"""
Compute the effective field using Fidimag and the tangents using
the NEB C code, according
to the improved NEB method, developed by Henkelman and Jonsson
# at: Henkelman et al., Journal of Chemical Physics 113, 22 (2000)
y :: The array with all the spin components for every image, i.e.
for a N images energy band and P spins system:
[theta0_0, phi0_0, theta0_1, phi0_1, ... , theta0_P, phi0_P,
theta1_0, phi1_0, ..., theta1_P, phi1_P,
...
thetaN_0, phiN_0, ..., thetaN_P, phiN_P]
"""
# Every row has all the spin components of an image
y.shape = (self.total_image_num, -1)
for i in range(self.image_num):
# Redefine the angles of the (i + 1)-th image
# (see the corresponding function)
check_boundary(y[i + 1])
# Set the simulation magnetisation to the (i+1)-th image
# spin components
self.sim.spin = spherical2cartesian(y[i + 1])
# Compute the effective field using Fidimag's methods.
# (we use the time=0 since we are only using the simulation
# object to get the field)
# Remember that The effective field is the gradient of
# the energy with respect to the generalised coordinates
# i.e. the magnetisation
self.sim.compute_effective_field(t=0)
h = self.sim.field
# Save the field components of the (i + 1)-th image
# to the effective field array which is in spherical coords
self.Heff[i + 1, :] = cartesian2spherical_field(h, y[i + 1])
# Compute and save the total energy for this image
self.energy[i + 1] = self.sim.compute_energy()
# Compute the 'distance' or difference between neighbouring states
# around the y[i+1] image. This is used to compute the spring force
dm1 = compute_dm(y[i], y[i + 1])
dm2 = compute_dm(y[i + 1], y[i + 2])
self.springs[i] = self.spring * (dm2 - dm1)
# Compute tangents using the C library (this is also used for
# cartesian coordinates, we set here the total number of spin
# components for spherical coords)
neb_clib.compute_tangents(y, self.energy, self.tangents,
self.total_image_num, 2 * self.n)
# Flatten y
y.shape = (-1, )
def sundials_rhs(self, time, y, ydot):
"""
Right hand side of the optimization scheme used to find the minimum
energy path. In our case, we use a LLG kind of equation:
d Y / dt = D
D = -( nabla E + [nabla E * t] t ) + F_spring
where Y is an image with P spins: Y = (M_0, ... , M_P) and t is the
tangent vector defined according to the energy of the neighbouring
images (see Henkelman et al publication)
If a climbing_image index is specified, the corresponding image will be
iterated without the spring force and with an inversed component along
the tangent
"""
# Update the ODE solver
self.ode_count += 1
# Compute the eff field H for every image, H = -nabla E
# (derived with respect to M)
self.compute_effective_field(y)
# Reshape y and ydot in a matrix of total_image_num rows
y.shape = (self.total_image_num, -1)
ydot.shape = (self.total_image_num, -1)
# Compute the total force for every image (not the extremes)
# Rememeber that self.image_num = self.total_image_num - 2
# The total force is:
# D = - (-nabla E + [nabla E * t] t) + F_spring
# This value is different is a climbing image is specified:
# D_climb = -nabla E + 2 * [nabla E * t] t
for i in range(self.image_num):
# The eff field has (i + 1) since it considers the extreme images
h = self.Heff[i + 1]
# Tangents and springs has length: total images -2 (no extremes)
t = self.tangents[i]
sf = self.springs[i]
if not (self.climbing_image and i == self.climbing_image):
h3 = h - np.dot(h, t) * t + sf * t
else:
h3 = h - 2 * np.dot(h, t) * t
# D vector for the i-th image (no extreme images)
ydot[i + 1, :] = h3[:]
# Extreme images do not have dynamics
ydot[0, :] = 0
ydot[-1, :] = 0
# Flatten the arrays
y.shape = (-1, )
ydot.shape = (-1, )
return 0
def compute_distance(self):
distance = []
ys = self.coords
ys.shape = (self.total_image_num, -1)
for i in range(self.total_image_num - 1):
dm = compute_dm(ys[i], ys[i + 1])
distance.append(dm)
ys.shape = (-1, )
self.distances = np.array(distance)
def run_until(self, t):
if t <= self.t:
return
self.integrator.run_until(t)
self.coords[:] = self.integrator.y[:]
m = self.coords
y = self.last_m
m.shape = (self.total_image_num, -1)
y.shape = (self.total_image_num, -1)
max_dmdt = 0
for i in range(1, self.image_num + 1):
dmdt = compute_dm(y[i], m[i]) / (t - self.t)
if dmdt > max_dmdt:
max_dmdt = dmdt
m.shape = (-1, )
y.shape = (-1, )
self.last_m[:] = m[:]
self.t = t
return max_dmdt
def relax(self,
dt=1e-8,
stopping_dmdt=1e4,
max_steps=1000,
save_npy_steps=100,
save_vtk_steps=100):
if self.integrator is None:
self.create_integrator()
log.debug("Relaxation parameters: "
"stopping_dmdt={} (degrees per nanosecond), "
"time_step={} s, max_steps={}.".format(
stopping_dmdt, dt, max_steps))
# Save the initial state i=0
self.compute_distance()
self.tablewriter.save()
self.tablewriter_dm.save()
for i in range(max_steps):
if i % save_vtk_steps == 0:
self.save_vtks()
if i % save_npy_steps == 0:
self.save_npys()
self.step += 1
cvode_dt = self.integrator.get_current_step()
increment_dt = dt
if cvode_dt > dt:
increment_dt = cvode_dt
dmdt = self.run_until(self.t + increment_dt)
self.compute_distance()
self.tablewriter.save()
self.tablewriter_dm.save()
log.debug("step: {:.3g}, step_size: {:.3g}"
" and max_dmdt: {:.3g}.".format(self.step, increment_dt,
dmdt))
if dmdt < stopping_dmdt:
break
log.info("Relaxation finished at time step = {:.4g}, "
"t = {:.2g}, call rhs = {:.4g} "
"and max_dmdt = {:.3g}".format(self.step, self.t,
self.ode_count, dmdt))
self.save_vtks()
self.save_npys()
class NEB_Sundials(object):
"""
Nudged elastic band method by solving the differential equation using Sundials.
"""
def __init__(self, sim,
initial_images,
climbing_image=None,
interpolations=None,
spring=5e5, name='unnamed'):
"""
*Arguments*
sim: the Simulation class
initial_images: a list contain the initial value, which can have
any of the forms accepted by the function 'finmag.util.helpers.
vector_valued_function', for example,
initial_images = [(0,0,1), (0,0,-1)]
or with given defined function
def init_m(pos):
x=pos[0]
if x<10:
return (0,1,1)
return (-1,0,0)
initial_images = [(0,0,1), (0,0,-1), init_m ]
are accepted forms.
climbing_image : An integer with the index (from 1 to the total
number of images minus two; it doesn't have any sense to use the
extreme images) of the image with the largest energy, which will
be updated in the NEB algorithm using the Climbing Image NEB
method (no spring force and "with the component along the elastic
band inverted" [*]). See: [*] Henkelman et al., The Journal of
Chemical Physics 113, 9901 (2000)
interpolations : a list only contain integers and the length of
this list should equal to the length of the initial_images minus
1, i.e., len(interpolations) = len(initial_images) - 1 ** THIS IS
not well defined in CARTESIAN coordinates**
spring: the spring constant, a float value
disable_tangent: this is an experimental option, by disabling the
tangent, we can get a rough feeling about the local energy minima
quickly.
"""
self.sim = sim
self.name = name
self.spring = spring
# We set a minus one because the *sundials_rhs* function
# only uses an array without counting the extreme images,
# whose length is self.image_num (see below)
if climbing_image is not None:
self.climbing_image = climbing_image - 1
else:
self.climbing_image = climbing_image
if interpolations is None:
interpolations = [0 for i in range(len(initial_images) - 1)]
self.initial_images = initial_images
self.interpolations = interpolations
if len(interpolations) != len(initial_images) - 1:
raise RuntimeError("""The length of interpolations should be equal to
the length of the initial_images array minus 1, i.e.,
len(interpolations) = len(initial_images) - 1""")
if len(initial_images) < 2:
raise RuntimeError("""At least two images must be provided
to create the energy band""")
# the total image number including two ends
self.total_image_num = len(initial_images) + sum(interpolations)
self.image_num = self.total_image_num - 2
# Number of nodes (spins)
self.n = sim.n
# Total number of spherical coordinates
# (2 components per spin for every image)
self.coords = np.zeros(2 * self.n * self.total_image_num)
self.last_m = np.zeros(self.coords.shape)
# For the effective field we use the extremes (to fit the energies
# array length). We could save some memory if we don't consider them
# (CHECK this in the future)
self.Heff = np.zeros(self.coords.shape)
# self.Heff = np.zeros(2 * self.n * self.total_image_num)
self.Heff.shape = (self.total_image_num, -1)
# Tangent components in spherical coordinates
self.tangents = np.zeros(2 * self.n * self.image_num)
self.tangents.shape = (self.image_num, -1)
self.energy = np.zeros(self.total_image_num)
self.springs = np.zeros(self.image_num)
self.pin_ids = np.array(
[i for i, v in enumerate(self.sim.pins) if v > 0], dtype=np.int32)
self.t = 0
self.step = 0
self.ode_count = 1
self.integrator = None
self.initial_image_coordinates()
self.create_tablewriter()
def create_tablewriter(self):
entities_energy = {
'step': {'unit': '<1>',
'get': lambda sim: sim.step,
'header': 'steps'},
'energy': {'unit': '<J>',
'get': lambda sim: sim.energy,
'header': ['image_%d' % i for i in range(self.image_num + 2)]}
}
self.tablewriter = DataSaver(
self, '%s_energy.ndt' % (self.name), entities=entities_energy)
entities_dm = {
'step': {'unit': '<1>',
'get': lambda sim: sim.step,
'header': 'steps'},
'dms': {'unit': '<1>',
'get': lambda sim: sim.distances,
'header': ['image_%d_%d' % (i, i + 1) for i in range(self.image_num + 1)]}
}
self.tablewriter_dm = DataSaver(
self, '%s_dms.ndt' % (self.name), entities=entities_dm)
def initial_image_coordinates(self):
"""
Generate the coordinates linearly according to the number of
interpolations provided.
Example: Imagine we have 4 images and we want 3 interpolations
between every neighbouring pair, i.e interpolations = [3, 3, 3]
1. Imagine the initial states with the interpolation numbers
and choose the first and second state
0 1 2 3
X -------- X --------- X -------- X
3 3 3
2. Counter image_id is set to 0
3. Set the image 0 magnetisation vector as m0 and append the
values to self.coords[0]. Update the counter: image_id = 1 now
4. Set the image 1 magnetisation values as m1 and interpolate
the values between m0 and m1, generating 3 arrays
with the magnetisation values of every interpolation image.
For every array, append the values to self.coords[i]
with i = 1, 2 and 3 ; updating the counter every time, so
image_id = 4 now
5. Append the value of m1 (image 1) in self.coords[4]
Update counter (image_id = 5 now)
6. Move to the next pair of images, now set the 1-th image
magnetisation values as m0 and append to self.coords[5]
7. Interpolate to get self.coords[i], for i = 6, 7, 8
...
8. Repeat as before until move to the pair of images: 2 - 3
9. Finally append the magnetisation of the last image
(self.initial_images[-1]). In this case, the 3rd image
Then, for every magnetisation vector values array (self.coords[i])
append the value to the simulation and store the energies
corresponding to every i-th image to the self.energy[i] arrays
Finally, flatten the self.coords matrix (containing the magnetisation
values of every image in different rows)
** Our generalised coordinates in the NEBM are the magnetisation values
*** Remember that the sim.spin object has the spins as:
[mx1, my1, mz1, mx2, my2, ... ]
and we transform to spherical coordinates as
[theta1, phi1, theta2, phi2, ... ]
Thus if we have N + 1 images and P + 1 spins, and naming
the i-th image coordinates as thetai_j, phii_j,
for the j-th spin, then the flattened array at the end is:
[theta0_0, phi0_0, theta0_1, phi0_1, ... ,
theta0_P, phi0_P, theta1_0, phi1_0, ...,
thetaN_0, phiN_0, ..., thetaN_P, phiN_P]
"""
# Initiate the counter
image_id = 0
self.coords.shape = (self.total_image_num, -1)
# For every interpolation between images (zero if no interpolations
# were specified)
for i in range(len(self.interpolations)):
# Store the number
n = self.interpolations[i]
# Save on the first image of a pair (step 1, 6, ...)
self.sim.set_m(self.initial_images[i])
m0 = self.sim.spin.copy()
# Save the spin components in spherical coordinates
self.coords[image_id][:] = cartesian2spherical(m0[:])
image_id = image_id + 1
# Set the second image in the pair as m1 and interpolate
# (step 4 and 7), saving in corresponding self.coords entries
self.sim.set_m(self.initial_images[i + 1])
m1 = self.sim.spin.copy()
# Interpolations (arrays with magnetisation values)
coords = linear_interpolation_two(m0, m1, n, self.pin_ids)
for coord in coords:
self.coords[image_id][:] = coord[:]
image_id = image_id + 1
# Continue to the next pair of images
# Append the magnetisation of the last image in spherical coords
self.sim.set_m(self.initial_images[-1])
m2 = self.sim.spin
self.coords[image_id][:] = cartesian2spherical(m2[:])
# Save the energies
for i in range(self.total_image_num):
self.sim.spin[:] = spherical2cartesian(self.coords[i][:])
self.sim.compute_effective_field(t=0)
self.energy[i] = self.sim.compute_energy()
# Flatten the array
self.coords.shape = (-1,)
def add_noise(self, T=0.1):
noise = T * np.random.rand(self.total_image_num, 3, self.n)
noise[:, :, self.pin_ids] = 0
noise[0, :, :] = 0
noise[-1, :, :] = 0
noise.shape = (-1,)
self.coords += noise
def save_vtks(self):
"""
Save vtk files in different folders, according to the
simulation name and step.
Files are saved as vtks/simname_simstep_vtk/image_00000x.vtk
"""
# Create the directory
directory = 'vtks/%s_%d' % (self.name, self.step)
self.vtk = SaveVTK(self.sim.mesh, directory)
self.coords.shape = (self.total_image_num, -1)
for i in range(self.total_image_num):
self.vtk.save_vtk(spherical2cartesian(self.coords[i]), step=i, vtkname='m')
self.coords.shape = (-1, )
def save_npys(self):
"""
Save npy files in different folders according to
the simulation name and step
Files are saved as: npys/simname_simstep/image_x.npy
"""
# Create directory as simname_simstep
directory = 'npys/%s_%d' % (self.name, self.step)
if not os.path.exists(directory):
os.makedirs(directory)
# Save the images with the format: 'image_{}.npy'
# where {} is the image number, starting from 0
self.coords.shape = (self.total_image_num, -1)
for i in range(self.total_image_num):
name = os.path.join(directory, 'image_%d.npy' % i)
np.save(name, spherical2cartesian(self.coords[i, :]))
self.coords.shape = (-1, )
def create_integrator(self, rtol=1e-6, atol=1e-6, nsteps=10000):
self.integrator = cvode.CvodeSolver(self.coords, self.sundials_rhs)
self.integrator.set_options(rtol, atol)
def compute_effective_field(self, y):
"""
Compute the effective field using Fidimag and the tangents using
the NEB C code, according
to the improved NEB method, developed by Henkelman and Jonsson
# at: Henkelman et al., Journal of Chemical Physics 113, 22 (2000)
y :: The array with all the spin components for every image, i.e.
for a N images energy band and P spins system:
[theta0_0, phi0_0, theta0_1, phi0_1, ... , theta0_P, phi0_P,
theta1_0, phi1_0, ..., theta1_P, phi1_P,
...
thetaN_0, phiN_0, ..., thetaN_P, phiN_P]
"""
# Every row has all the spin components of an image
y.shape = (self.total_image_num, -1)
for i in range(self.image_num):
# Redefine the angles of the (i + 1)-th image
# (see the corresponding function)
check_boundary(y[i + 1])
# Set the simulation magnetisation to the (i+1)-th image
# spin components
self.sim.spin = spherical2cartesian(y[i + 1])
# Compute the effective field using Fidimag's methods.
# (we use the time=0 since we are only using the simulation
# object to get the field)
# Remember that The effective field is the gradient of
# the energy with respect to the generalised coordinates
# i.e. the magnetisation
self.sim.compute_effective_field(t=0)
h = self.sim.field
# Save the field components of the (i + 1)-th image
# to the effective field array which is in spherical coords
self.Heff[i + 1, :] = cartesian2spherical_field(h, y[i + 1])
# Compute and save the total energy for this image
self.energy[i + 1] = self.sim.compute_energy()
# Compute the 'distance' or difference between neighbouring states
# around the y[i+1] image. This is used to compute the spring force
dm1 = compute_dm(y[i], y[i + 1])
dm2 = compute_dm(y[i + 1], y[i + 2])
self.springs[i] = self.spring * (dm2 - dm1)
# Compute tangents using the C library (this is also used for
# cartesian coordinates, we set here the total number of spin
# components for spherical coords)
neb_clib.compute_tangents(
y, self.energy, self.tangents, self.total_image_num, 2 * self.n)
# Flatten y
y.shape = (-1, )
def sundials_rhs(self, time, y, ydot):
"""
Right hand side of the optimization scheme used to find the minimum
energy path. In our case, we use a LLG kind of equation:
d Y / dt = D
D = -( nabla E + [nabla E * t] t ) + F_spring
where Y is an image with P spins: Y = (M_0, ... , M_P) and t is the
tangent vector defined according to the energy of the neighbouring
images (see Henkelman et al publication)
If a climbing_image index is specified, the corresponding image will be
iterated without the spring force and with an inversed component along
the tangent
"""
# Update the ODE solver
self.ode_count += 1
# Compute the eff field H for every image, H = -nabla E
# (derived with respect to M)
self.compute_effective_field(y)
# Reshape y and ydot in a matrix of total_image_num rows
y.shape = (self.total_image_num, -1)
ydot.shape = (self.total_image_num, -1)
# Compute the total force for every image (not the extremes)
# Rememeber that self.image_num = self.total_image_num - 2
# The total force is:
# D = - (-nabla E + [nabla E * t] t) + F_spring
# This value is different is a climbing image is specified:
# D_climb = -nabla E + 2 * [nabla E * t] t
for i in range(self.image_num):
# The eff field has (i + 1) since it considers the extreme images
h = self.Heff[i + 1]
# Tangents and springs has length: total images -2 (no extremes)
t = self.tangents[i]
sf = self.springs[i]
if not (self.climbing_image and i == self.climbing_image):
h3 = h - np.dot(h, t) * t + sf * t
else:
h3 = h - 2 * np.dot(h, t) * t
# D vector for the i-th image (no extreme images)
ydot[i + 1, :] = h3[:]
# Extreme images do not have dynamics
ydot[0, :] = 0
ydot[-1, :] = 0
# Flatten the arrays
y.shape = (-1,)
ydot.shape = (-1,)
return 0
def compute_distance(self):
distance = []
ys = self.coords
ys.shape = (self.total_image_num, -1)
for i in range(self.total_image_num - 1):
dm = compute_dm(ys[i], ys[i + 1])
distance.append(dm)
ys.shape = (-1, )
self.distances = np.array(distance)
def run_until(self, t):
if t <= self.t:
return
self.integrator.run_until(t)
self.coords[:] = self.integrator.y[:]
m = self.coords
y = self.last_m
m.shape = (self.total_image_num, -1)
y.shape = (self.total_image_num, -1)
max_dmdt = 0
for i in range(1, self.image_num + 1):
dmdt = compute_dm(y[i], m[i]) / (t - self.t)
if dmdt > max_dmdt:
max_dmdt = dmdt
m.shape = (-1,)
y.shape = (-1,)
self.last_m[:] = m[:]
self.t = t
return max_dmdt
def relax(self, dt=1e-8, stopping_dmdt=1e4,
max_steps=1000, save_npy_steps=100,
save_vtk_steps=100):
if self.integrator is None:
self.create_integrator()
log.debug("Relaxation parameters: "
"stopping_dmdt={} (degrees per nanosecond), "
"time_step={} s, max_steps={}.".format(stopping_dmdt,
dt, max_steps))
# Save the initial state i=0
self.compute_distance()
self.tablewriter.save()
self.tablewriter_dm.save()
for i in range(max_steps):
if i % save_vtk_steps == 0:
self.save_vtks()
if i % save_npy_steps == 0:
self.save_npys()
self.step += 1
cvode_dt = self.integrator.get_current_step()
increment_dt = dt
if cvode_dt > dt:
increment_dt = cvode_dt
dmdt = self.run_until(self.t + increment_dt)
self.compute_distance()
self.tablewriter.save()
self.tablewriter_dm.save()
log.debug("step: {:.3g}, step_size: {:.3g}"
" and max_dmdt: {:.3g}.".format(self.step,
increment_dt,
dmdt))
if dmdt < stopping_dmdt:
break
log.info("Relaxation finished at time step = {:.4g}, "
"t = {:.2g}, call rhs = {:.4g} "
"and max_dmdt = {:.3g}".format(self.step,
self.t,
self.ode_count,
dmdt))
self.save_vtks()
self.save_npys()
