def scp(p,bad_constr,sol):
"""
Description: Sequential convex programming
algorithm. Solve program p and try to
enforce equality on the bad constraints.
Argument p: cvxpy_program is assumed to be in
expanded and equivalent format.
Argument bad_constr: List of nonconvex
constraints, also in expanded and equivalent
format.
Argument sol: Solution of relaxation.
"""
# Quit if program is linear
if(len(bad_constr) == 0):
if(not p.options['quiet']):
print 'Tightening not needed'
return True
# Get parameters
tight_tol = p.options['SCP_ALG']['tight tol']
starting_lambda = p.options['SCP_ALG']['starting lambda']
max_scp_iter = p.options['SCP_ALG']['max scp iter']
lambda_multiplier = p.options['SCP_ALG']['lambda multiplier']
max_lambda = p.options['SCP_ALG']['max lambda']
top_residual = p.options['SCP_ALG']['top residual']
# Construct slacks
slacks = [abs(c.left-c.right) for c in bad_constr]
# Print header
if(not p.options['quiet']):
print 'Iter\t:',
print 'Max Slack\t:',
print 'Objective\t:',
print 'Solver Status\t:',
print 'Pres\t\t:',
print 'Dres\t\t:',
print 'Lambda Max/Min'
# SCP Loop
lam = starting_lambda*np.ones(len(slacks))
for i in range(0,max_scp_iter,1):
# Calculate max slack
max_slack = max(map(lambda x:x.get_value(), slacks))
# Quit if status is primal infeasible
if(sol['status'] == 'primal infeasible'):
if(not p.options['quiet']):
print 'Unable to tighten: Problem became infeasible'
return False
# Check if dual infeasible
if(sol['status'] == 'dual infeasible'):
sol['status'] = 'dual inf'
sol['primal infeasibility'] = np.NaN
sol['dual infeasibility'] = np.NaN
# Print values
if(not p.options['quiet']):
print '%d\t:' %i,
print '%.3e\t:' %max_slack,
print '%.3e\t:' %p.obj.get_value(),
print ' '+sol['status']+'\t:',
if(sol['primal infeasibility'] is not np.NaN):
print '%.3e\t:' %sol['primal infeasibility'],
else:
print '%.3e\t\t:' %sol['primal infeasibility'],
if(sol['dual infeasibility'] is not np.NaN):
print '%.3e\t:' %sol['dual infeasibility'],
else:
print '%.3e\t\t:' %sol['dual infeasibility'],
print '(%.1e,%.1e)' %(np.max(lam),np.min(lam))
# Quit if max slack is small
if(max_slack < tight_tol and
sol['status'] == 'optimal'):
if(not p.options['quiet']):
print 'Tightening successful'
return True
# Quit if residual is too large
if(sol['primal infeasibility'] >= top_residual or
sol['dual infeasibility'] >= top_residual):
if(not p.options['quiet']):
print 'Unable to tighten: Residuals are too large'
return False
# Linearize slacks
linear_slacks = []
for c in bad_constr:
fn = c.left.item
args = c.left.children
right = c.right
line = fn._linearize(args,right)
linear_slacks += [line]
# Add linearized slacks to objective
sum_lin_slacks = 0.0
for j in range(0,len(slacks),1):
sum_lin_slacks += lam[j]*linear_slacks[j]
if(p.action == MINIMIZE):
new_obj = p.obj + sum_lin_slacks
else:
new_obj = p.obj - sum_lin_slacks
new_t0, obj_constr = expand(new_obj)
new_p = prog((p.action,new_t0), obj_constr+p.constr,[],p.options)
# Solve new problem
sol = solve_convex(new_p,'scp')
# Update lambdas
for j in range(0,len(slacks),1):
if(slacks[j].get_value() >= tight_tol):
if(lam[j] < max_lambda):
lam[j] = lam[j]*lambda_multiplier
# Maxiters reached
if(not p.options['quiet']):
print 'Unable to tighten: Maximum iterations reached'
if(sol['status'] == 'optimal'):
return True
else:
return False
def solve_prog(p):
"""
Description
-----------
Solve optimization program.
Arguments
---------
p: cvxpy_program
"""
# Reset variable counter
var_reset()
# Check parameters
if (len(p.get_params()) != 0):
if (not p.options['quiet']):
print 'Error: Parameters present'
return np.NaN, np.NaN
# Original
if (p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Original *'
print '****************************'
p.show()
# Expanded
p_expanded = p._get_expanded()
if (p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Expanded *'
print '****************************'
p_expanded.show()
# Equivalent
p_equivalent = p_expanded._get_equivalent()
if (p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Equivalent *'
print '****************************'
p_equivalent.show()
# Nonconvex constraints
bad_constr = p_equivalent.constr._get_nonconvex()
if (p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Nonconvex Constraints *'
print '****************************\n'
print bad_constr
# Convex Relaxation
p_cvx_relaxation = p_equivalent._get_cvx_relaxation()
if (p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Convex Relaxation *'
print '****************************'
p_cvx_relaxation.show()
# Solve convex relaxation
if (not p.options['quiet']):
print '\nSolving convex relaxation ...'
sol = solve_convex(p_cvx_relaxation, 'rel')
lagrange_mul_eq = matrix(sol['y'])
if (not p.options['quiet']):
print 'Relaxation status: ', sol['status']
# Relaxation status: primal infeasible
if (sol['status'] == 'primal infeasible'):
if (not p.options['quiet']):
print 'Original program is primal infeasible'
if (p.action == MINIMIZE):
return np.inf, lagrange_mul_eq
else:
return -np.inf, lagrange_mul_eq
# Relaxation status: uknown
elif (sol['status'] == 'unknown'):
relaxation_obj = None
# Relaxation status: dual infeasible
elif (sol['status'] == 'dual infeasible'):
if (p.action == MINIMIZE):
relaxation_obj = -np.inf
else:
relaxation_obj = np.inf
# Relaxacion status: optimal
else:
relaxation_obj = p_cvx_relaxation.obj.get_value()
# Report max slack
if (len(bad_constr) != 0 and not p.options['quiet']):
print 'Max Slack: ',
print max(
map(lambda x: x.get_value(),
[abs(c.left - c.right) for c in bad_constr]))
# Tighten
if (p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Tightening Stage *'
print '****************************'
elif (not p.options['quiet']):
print '\nAttempting tightening ...'
valid_scp = scp(p_cvx_relaxation, bad_constr, sol)
if (not valid_scp):
return np.NaN, np.NaN
# Prepare results
if (len(bad_constr) == 0):
obj = relaxation_obj
else:
obj = p.obj.get_value()
if (p.action == MINIMIZE):
bound_str = 'Lower Bound'
if (relaxation_obj != None):
bound = np.min([relaxation_obj, obj])
gap = np.max([obj - relaxation_obj, 0.0])
else:
bound_str = 'Upper Bound'
if (relaxation_obj != None):
bound = np.max([relaxation_obj, obj])
gap = np.max([relaxation_obj - obj, 0.0])
# Show results
if (p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Results *'
print '****************************'
elif (not p.options['quiet']):
print '\nResults'
if (not p.options['quiet']):
print 'Objective =\t%.5e' % obj
if (relaxation_obj != None):
print bound_str + ' =\t%.5e' % bound
print 'Gap =\t\t%.5e' % gap
else:
print bound_str + ' =\tUnknown'
print 'Gap =\t\tUnknown'
if (len(bad_constr) != 0):
ms = max(
map(lambda x: x.get_value(),
[abs(c.left - c.right) for c in bad_constr]))
print 'Max Slack =\t%.5e' % ms
# Return objective and dual var
return obj, lagrange_mul_eq
def solve_prog(p):
"""
Description
-----------
Solve optimization program.
Arguments
---------
p: cvxpy_program
"""
# Reset variable counter
var_reset()
# Check parameters
if(len(p.get_params()) != 0):
if(not p.options['quiet']):
print 'Error: Parameters present'
return np.NaN,np.NaN
# Original
if(p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Original *'
print '****************************'
p.show()
# Expanded
p_expanded = p._get_expanded()
if(p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Expanded *'
print '****************************'
p_expanded.show()
# Equivalent
p_equivalent = p_expanded._get_equivalent()
if(p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Equivalent *'
print '****************************'
p_equivalent.show()
# Nonconvex constraints
bad_constr = p_equivalent.constr._get_nonconvex()
if(p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Nonconvex Constraints *'
print '****************************\n'
print bad_constr
# Convex Relaxation
p_cvx_relaxation = p_equivalent._get_cvx_relaxation()
if(p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Convex Relaxation *'
print '****************************'
p_cvx_relaxation.show()
# Solve convex relaxation
if(not p.options['quiet']):
print '\nSolving convex relaxation ...'
sol = solve_convex(p_cvx_relaxation,'rel')
lagrange_mul_eq = matrix(sol['y'])
if(not p.options['quiet']):
print 'Relaxation status: ',sol['status']
# Relaxation status: primal infeasible
if(sol['status'] == 'primal infeasible'):
if(not p.options['quiet']):
print 'Original program is primal infeasible'
if(p.action == MINIMIZE):
return np.inf,lagrange_mul_eq
else:
return -np.inf,lagrange_mul_eq
# Relaxation status: uknown
elif(sol['status'] == 'unknown'):
relaxation_obj = None
# Relaxation status: dual infeasible
elif(sol['status'] == 'dual infeasible'):
if(p.action == MINIMIZE):
relaxation_obj = -np.inf
else:
relaxation_obj = np.inf
# Relaxacion status: optimal
else:
relaxation_obj = p_cvx_relaxation.obj.get_value()
# Report max slack
if(len(bad_constr) != 0 and not p.options['quiet']):
print 'Max Slack: ',
print max(map(lambda x:x.get_value(),
[abs(c.left-c.right) for c in bad_constr]))
# Tighten
if(p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Tightening Stage *'
print '****************************'
elif(not p.options['quiet']):
print '\nAttempting tightening ...'
valid_scp = scp(p_cvx_relaxation,bad_constr,sol)
if(not valid_scp):
return np.NaN,np.NaN
# Prepare results
if(len(bad_constr) == 0):
obj = relaxation_obj
else:
obj = p.obj.get_value()
if(p.action == MINIMIZE):
bound_str = 'Lower Bound'
if(relaxation_obj != None):
bound = np.min([relaxation_obj,obj])
gap = np.max([obj-relaxation_obj,0.0])
else:
bound_str = 'Upper Bound'
if(relaxation_obj != None):
bound = np.max([relaxation_obj,obj])
gap = np.max([relaxation_obj-obj,0.0])
# Show results
if(p.options['show steps'] and not p.options['quiet']):
print '\n'
print '****************************'
print '* Results *'
print '****************************'
elif(not p.options['quiet']):
print '\nResults'
if(not p.options['quiet']):
print 'Objective =\t%.5e' %obj
if(relaxation_obj != None):
print bound_str+' =\t%.5e' %bound
print 'Gap =\t\t%.5e' %gap
else:
print bound_str+' =\tUnknown'
print 'Gap =\t\tUnknown'
if(len(bad_constr) != 0):
ms = max(map(lambda x:x.get_value(),
[abs(c.left-c.right) for c in bad_constr]))
print 'Max Slack =\t%.5e' %ms
# Return objective and dual var
return obj,lagrange_mul_eq
