"""
Copied and modified from https://github.com/UW-ERSL/AuTO
Under GNU General Public License v3.0
Original copy from https://github.com/arjendeetman/GCMMA-MMA-Python/blob/master/Code/MMA.py
Improvement is made to avoid N^2 memory operation so that the MMA solver is more scalable.
"""
from numpy import diag as diags
from numpy.linalg import solve
import numpy as np
import jax
import jax.numpy as jnp
from jax import jit, grad, random, jacfwd, value_and_grad
from functools import partial
import time
import scipy
from jax.experimental.sparse import BCOO
from jax import config
config.update("jax_enable_x64", True)
density_filtering = False
sensitivity_filtering = True
def compute_filter_kd_tree(fe):
"""This function is created by Tianju. Not from the original code.
We use k-d tree algorithm to compute the filter.
"""
cell_centroids = np.mean(np.take(fe.points, fe.cells, axis=0), axis=1)
flex_num_cells = len(fe.flex_inds)
flex_cell_centroids = np.take(cell_centroids, fe.flex_inds, axis=0)
V = np.sum(fe.JxW)
avg_elem_V = V/fe.num_cells
avg_elem_size = avg_elem_V**(1./fe.dim)
rmin = 1.5*avg_elem_size
kd_tree = scipy.spatial.KDTree(flex_cell_centroids)
I = []
J = []
V = []
for i in range(flex_num_cells):
num_nbs = 20
dd, ii = kd_tree.query(flex_cell_centroids[i], num_nbs)
neighbors = np.take(flex_cell_centroids, ii, axis=0)
vals = np.where(rmin - dd > 0., rmin - dd, 0.)
I += [i]*num_nbs
J += ii.tolist()
V += vals.tolist()
H_sp = scipy.sparse.csc_array((V, (I, J)), shape=(flex_num_cells, flex_num_cells))
H = BCOO.from_scipy_sparse(H_sp).sort_indices()
Hs = H.sum(1).todense()
return H, Hs
def applySensitivityFilter(ft, rho, dJ, dvc):
dJ = ft['H'] @ (rho*dJ/np.maximum(1e-3, rho)/ft['Hs'][:, None])
dvc = ft['H'][None, :, :] @ (rho[None, :, :]*dvc/np.maximum(1e-3, rho[None, :, :])/ft['Hs'][None, :, None])
return dJ, dvc
def applyDensityFilter(ft, rho):
return ft['H'] @ rho / ft['Hs'][:, None]
#%% Optimizer
class MMA:
# The code was modified from [MMA Svanberg 1987]. Please cite the paper if
# you end up using this code.
def __init__(self):
self.epoch = 0;
def resetMMACounter(self):
self.epoch = 0;
def registerMMAIter(self, xval, xold1, xold2):
self.epoch += 1;
self.xval = xval;
self.xold1 = xold1;
self.xold2 = xold2;
def setNumConstraints(self, numConstraints):
self.numConstraints = numConstraints;
def setNumDesignVariables(self, numDesVar):
self.numDesignVariables = numDesVar;
def setMinandMaxBoundsForDesignVariables(self, xmin, xmax):
self.xmin = xmin;
self.xmax = xmax;
def setObjectiveWithGradient(self, obj, objGrad):
self.objective = obj;
self.objectiveGradient = objGrad;
def setConstraintWithGradient(self, cons, consGrad):
self.constraint = cons;
self.consGrad = consGrad;
def setScalingParams(self, zconst, zscale, ylinscale, yquadscale):
self.zconst = zconst;
self.zscale = zscale;
self.ylinscale = ylinscale;
self.yquadscale = yquadscale;
def setMoveLimit(self, movelim):
self.moveLimit = movelim;
def setLowerAndUpperAsymptotes(self, low, upp):
self.lowAsymp = low;
self.upAsymp = upp;
def getOptimalValues(self):
return self.xmma, self.ymma, self.zmma;
def getLagrangeMultipliers(self):
return self.lam, self.xsi, self.eta, self.mu, self.zet;
def getSlackValue(self):
return self.slack;
def getAsymptoteValues(self):
return self.lowAsymp, self.upAsymp;
# Function for the MMA sub problem
def mmasub(self, xval):
m = self.numConstraints;
n = self.numDesignVariables;
iter = self.epoch;
xmin, xmax = self.xmin, self.xmax;
xold1, xold2 = self.xold1, self.xold2;
f0val, df0dx = self.objective, self.objectiveGradient;
fval, dfdx = self.constraint, self.consGrad;
low, upp = self.lowAsymp, self.upAsymp;
a0, a, c, d = self.zconst, self.zscale, self.ylinscale, self.yquadscale;
move = self.moveLimit;
epsimin = 0.0000001
raa0 = 0.00001
albefa = 0.1
asyinit = 0.5
asyincr = 1.2
asydecr = 0.7
eeen = np.ones((n, 1))
eeem = np.ones((m, 1))
zeron = np.zeros((n, 1))
# Calculation of the asymptotes low and upp
if iter <= 2:
low = xval-asyinit*(xmax-xmin)
upp = xval+asyinit*(xmax-xmin)
else:
zzz = (xval-xold1)*(xold1-xold2)
factor = eeen.copy()
factor[np.where(zzz>0)] = asyincr
factor[np.where(zzz<0)] = asydecr
low = xval-factor*(xold1-low)
upp = xval+factor*(upp-xold1)
lowmin = xval-10*(xmax-xmin)
lowmax = xval-0.01*(xmax-xmin)
uppmin = xval+0.01*(xmax-xmin)
uppmax = xval+10*(xmax-xmin)
low = np.maximum(low,lowmin)
low = np.minimum(low,lowmax)
upp = np.minimum(upp,uppmax)
upp = np.maximum(upp,uppmin)
# Calculation of the bounds alfa and beta
zzz1 = low+albefa*(xval-low)
zzz2 = xval-move*(xmax-xmin)
zzz = np.maximum(zzz1,zzz2)
alfa = np.maximum(zzz,xmin)
zzz1 = upp-albefa*(upp-xval)
zzz2 = xval+move*(xmax-xmin)
zzz = np.minimum(zzz1,zzz2)
beta = np.minimum(zzz,xmax)
# Calculations of p0, q0, P, Q and b
xmami = xmax-xmin
xmamieps = 0.00001*eeen
xmami = np.maximum(xmami,xmamieps)
xmamiinv = eeen/xmami
ux1 = upp-xval
ux2 = ux1*ux1
xl1 = xval-low
xl2 = xl1*xl1
uxinv = eeen/ux1
xlinv = eeen/xl1
p0 = zeron.copy()
q0 = zeron.copy()
p0 = np.maximum(df0dx,0)
q0 = np.maximum(-df0dx,0)
pq0 = 0.001*(p0+q0)+raa0*xmamiinv
p0 = p0+pq0
q0 = q0+pq0
p0 = p0*ux2
q0 = q0*xl2
P = np.zeros((m,n)) ## @@ make sparse with scipy?
Q = np.zeros((m,n)) ## @@ make sparse with scipy?
P = np.maximum(dfdx,0)
Q = np.maximum(-dfdx,0)
PQ = 0.001*(P+Q)+raa0*np.dot(eeem,xmamiinv.T)
P = P+PQ
Q = Q+PQ
# P = (diags(ux2.flatten(),0).dot(P.T)).T
# Q = (diags(xl2.flatten(),0).dot(Q.T)).T
P = ux2.T*P
Q = xl2.T*Q
b = (np.dot(P,uxinv)+np.dot(Q,xlinv)-fval)
# Solving the subproblem by a primal-dual Newton method
xmma,ymma,zmma,lam,xsi,eta,mu,zet,s = subsolv(m,n,epsimin,low,upp,alfa,\
beta,p0,q0,P,Q,a0,a,b,c,d)
# Return values
self.xmma, self.ymma, self.zmma = xmma, ymma, zmma;
self.lam, self.xsi, self.eta, self.mu, self.zet = lam,xsi,eta,mu,zet;
self.slack = s;
self.lowAsymp, self.upAsymp = low, upp;
def subsolv(m,n,epsimin,low,upp,alfa,beta,p0,q0,P,Q,a0,a,b,c,d):
een = np.ones((n,1))
eem = np.ones((m,1))
epsi = 1
epsvecn = epsi*een
epsvecm = epsi*eem
x = 0.5*(alfa+beta)
y = eem.copy()
z = np.array([[1.0]])
lam = eem.copy()
xsi = een/(x-alfa)
xsi = np.maximum(xsi,een)
eta = een/(beta-x)
eta = np.maximum(eta,een)
mu = np.maximum(eem,0.5*c)
zet = np.array([[1.0]])
s = eem.copy()
itera = 0
# Start while epsi>epsimin
while epsi > epsimin:
epsvecn = epsi*een
epsvecm = epsi*eem
ux1 = upp-x
xl1 = x-low
ux2 = ux1*ux1
xl2 = xl1*xl1
uxinv1 = een/ux1
xlinv1 = een/xl1
plam = p0+np.dot(P.T,lam)
qlam = q0+np.dot(Q.T,lam)
gvec = np.dot(P,uxinv1)+np.dot(Q,xlinv1)
dpsidx = plam/ux2-qlam/xl2
rex = dpsidx-xsi+eta
rey = c+d*y-mu-lam
rez = a0-zet-np.dot(a.T,lam)
relam = gvec-a*z-y+s-b
rexsi = xsi*(x-alfa)-epsvecn
reeta = eta*(beta-x)-epsvecn
remu = mu*y-epsvecm
rezet = zet*z-epsi
res = lam*s-epsvecm
residu1 = np.concatenate((rex, rey, rez), axis = 0)
residu2 = np.concatenate((relam, rexsi, reeta, remu, rezet, res), axis = 0)
residu = np.concatenate((residu1, residu2), axis = 0)
residunorm = np.sqrt((np.dot(residu.T,residu)).item())
residumax = np.max(np.abs(residu))
ittt = 0
# Start while (residumax>0.9*epsi) and (ittt<200)
while (residumax > 0.9*epsi) and (ittt < 200):
ittt = ittt+1
itera = itera+1
ux1 = upp-x
xl1 = x-low
ux2 = ux1*ux1
xl2 = xl1*xl1
ux3 = ux1*ux2
xl3 = xl1*xl2
uxinv1 = een/ux1
xlinv1 = een/xl1
uxinv2 = een/ux2
xlinv2 = een/xl2
plam = p0+np.dot(P.T,lam)
qlam = q0+np.dot(Q.T,lam)
gvec = np.dot(P,uxinv1)+np.dot(Q,xlinv1)
# GG = (diags(uxinv2.flatten(),0).dot(P.T)).T-(diags\
# (xlinv2.flatten(),0).dot(Q.T)).T
GG = uxinv2.T*P - xlinv2.T*Q
dpsidx = plam/ux2-qlam/xl2
delx = dpsidx-epsvecn/(x-alfa)+epsvecn/(beta-x)
dely = c+d*y-lam-epsvecm/y
delz = a0-np.dot(a.T,lam)-epsi/z
dellam = gvec-a*z-y-b+epsvecm/lam
diagx = plam/ux3+qlam/xl3
diagx = 2*diagx+xsi/(x-alfa)+eta/(beta-x)
diagxinv = een/diagx
diagy = d+mu/y
diagyinv = eem/diagy
diaglam = s/lam
diaglamyi = diaglam+diagyinv
# Start if m<n
if m < n:
blam = dellam+dely/diagy-np.dot(GG,(delx/diagx))
bb = np.concatenate((blam,delz),axis = 0)
# Alam = np.asarray(diags(diaglamyi.flatten(),0) \
# +(diags(diagxinv.flatten(),0).dot(GG.T).T).dot(GG.T))
Alam = diags(diaglamyi.flatten(),0) + (diagxinv.T*GG).dot(GG.T)
AAr1 = np.concatenate((Alam,a),axis = 1)
AAr2 = np.concatenate((a,-zet/z),axis = 0).T
AA = np.concatenate((AAr1,AAr2),axis = 0)
solut = solve(AA,bb)
dlam = solut[0:m]
dz = solut[m:m+1]
dx = -delx/diagx-np.dot(GG.T,dlam)/diagx
else:
diaglamyiinv = eem/diaglamyi
dellamyi = dellam+dely/diagy
Axx = np.asarray(diags(diagx.flatten(),0) \
+(diags(diaglamyiinv.flatten(),0).dot(GG).T).dot(GG))
azz = zet/z+np.dot(a.T,(a/diaglamyi))
axz = np.dot(-GG.T,(a/diaglamyi))
bx = delx+np.dot(GG.T,(dellamyi/diaglamyi))
bz = delz-np.dot(a.T,(dellamyi/diaglamyi))
AAr1 = np.concatenate((Axx,axz),axis = 1)
AAr2 = np.concatenate((axz.T,azz),axis = 1)
AA = np.concatenate((AAr1,AAr2),axis = 0)
bb = np.concatenate((-bx,-bz),axis = 0)
solut = solve(AA,bb)
dx = solut[0:n]
dz = solut[n:n+1]
dlam = np.dot(GG,dx)/diaglamyi-dz*(a/diaglamyi)\
+dellamyi/diaglamyi
# End if m<n
dy = -dely/diagy+dlam/diagy
dxsi = -xsi+epsvecn/(x-alfa)-(xsi*dx)/(x-alfa)
deta = -eta+epsvecn/(beta-x)+(eta*dx)/(beta-x)
dmu = -mu+epsvecm/y-(mu*dy)/y
dzet = -zet+epsi/z-zet*dz/z
ds = -s+epsvecm/lam-(s*dlam)/lam
xx = np.concatenate((y,z,lam,xsi,eta,mu,zet,s),axis = 0)
dxx = np.concatenate((dy,dz,dlam,dxsi,deta,dmu,dzet,ds),axis = 0)
#
stepxx = -1.01*dxx/xx
stmxx = np.max(stepxx)
stepalfa = -1.01*dx/(x-alfa)
stmalfa = np.max(stepalfa)
stepbeta = 1.01*dx/(beta-x)
stmbeta = np.max(stepbeta)
stmalbe = max(stmalfa,stmbeta)
stmalbexx = max(stmalbe,stmxx)
stminv = max(stmalbexx,1.0)
steg = 1.0/stminv
#
xold = x.copy()
yold = y.copy()
zold = z.copy()
lamold = lam.copy()
xsiold = xsi.copy()
etaold = eta.copy()
muold = mu.copy()
zetold = zet.copy()
sold = s.copy()
#
itto = 0
resinew = 2*residunorm
# Start: while (resinew>residunorm) and (itto<50)
while (resinew > residunorm) and (itto < 50):
itto = itto+1
x = xold+steg*dx
y = yold+steg*dy
z = zold+steg*dz
lam = lamold+steg*dlam
xsi = xsiold+steg*dxsi
eta = etaold+steg*deta
mu = muold+steg*dmu
zet = zetold+steg*dzet
s = sold+steg*ds
ux1 = upp-x
xl1 = x-low
ux2 = ux1*ux1
xl2 = xl1*xl1
uxinv1 = een/ux1
xlinv1 = een/xl1
plam = p0+np.dot(P.T,lam)
qlam = q0+np.dot(Q.T,lam)
gvec = np.dot(P,uxinv1)+np.dot(Q,xlinv1)
dpsidx = plam/ux2-qlam/xl2
rex = dpsidx-xsi+eta
rey = c+d*y-mu-lam
rez = a0-zet-np.dot(a.T,lam)
relam = gvec-np.dot(a,z)-y+s-b
rexsi = xsi*(x-alfa)-epsvecn
reeta = eta*(beta-x)-epsvecn
remu = mu*y-epsvecm
rezet = np.dot(zet,z)-epsi
res = lam*s-epsvecm
residu1 = np.concatenate((rex,rey,rez),axis = 0)
residu2 = np.concatenate((relam,rexsi,reeta,remu,rezet,res), \
axis = 0)
residu = np.concatenate((residu1,residu2),axis = 0)
resinew = np.sqrt(np.dot(residu.T,residu))
steg = steg/2
# End: while (resinew>residunorm) and (itto<50)
residunorm = resinew.copy()
residumax = max(abs(residu))
steg = 2*steg
# End: while (residumax>0.9*epsi) and (ittt<200)
epsi = 0.1*epsi
# End: while epsi>epsimin
xmma = x.copy()
ymma = y.copy()
zmma = z.copy()
lamma = lam
xsimma = xsi
etamma = eta
mumma = mu
zetmma = zet
smma = s
return xmma,ymma,zmma,lamma,xsimma,etamma,mumma,zetmma,smma
[docs]
def optimize(fe, rho_ini, optimizationParams, objectiveHandle, consHandle, numConstraints):
"""
Performs topology optimization using the Method of Moving Asymptotes (MMA).
Parameters
----------
fe : FiniteElement
Finite element object.
rho_ini : NumpyArray
Initial density distribution.
Shape is (num_rho_vars, 1).
optimizationParams : dict
Dictionary containing optimization parameters:
- 'movelimit': Move limit for design variables (float)
- 'maxIters': Maximum number of iterations (int)
objectiveHandle : callable
Function that computes the objective value and its gradient.
Signature: ``J, dJ = objectiveHandle(rho_physical)``
- ``rho_physical``: Physical density field (filtered if enabled). Same shape as ``rho_ini``.
- ``J``: Objective value (scalar).
- ``dJ``: Objective gradient (NumpyArray, same shape as ``rho_ini``).
consHandle : callable
Function that computes constraint values and their gradients.
Signature: ``vc, dvc = consHandle(rho_physical, iter)``
- ``rho_physical``: Physical density field (filtered if enabled). Same shape as ``rho_ini``.
- ``iter``: Current optimization iteration (int).
- ``vc``: Constraint values. Shape is (num_constraints,).
- ``dvc``: Constraint gradients. Shape is (num_constraints, ...), where ... shares the same shape with ``rho_ini``.
numConstraints : int
Number of constraints in the optimization problem.
Returns
-------
rho : NumpyArray
Optimized density distribution after completing all iterations.
Same shape as ``rho_ini``.
Notes
-----
TODO: Scale objective function value to be always within 1-100
(`ref <https://doi.org/10.1016/j.compstruc.2018.01.008>`_).
"""
H, Hs = compute_filter_kd_tree(fe)
ft = {'H':H, 'Hs':Hs}
rho = rho_ini
loop = 0
m = numConstraints # num constraints
n = len(rho.reshape(-1)) # num params
mma = MMA()
mma.setNumConstraints(numConstraints)
mma.setNumDesignVariables(n)
mma.setMinandMaxBoundsForDesignVariables\
(np.zeros((n,1)),np.ones((n,1)))
xval = rho.reshape(-1)[:, None]
xold1, xold2 = xval.copy(), xval.copy()
mma.registerMMAIter(xval, xold1, xold2)
mma.setLowerAndUpperAsymptotes(np.ones((n,1)), np.ones((n,1)))
mma.setScalingParams(1.0, np.zeros((m,1)), \
10000*np.ones((m,1)), np.zeros((m,1)))
# Move limit is an important parameter that affects TO result; default can be 0.2
mma.setMoveLimit(optimizationParams['movelimit'])
while loop < optimizationParams['maxIters']:
loop = loop + 1
print(f"MMA solver...")
if density_filtering:
rho_physical = applyDensityFilter(ft, rho)
else:
rho_physical = rho
J, dJ = objectiveHandle(rho_physical)
vc, dvc = consHandle(rho_physical, loop)
if sensitivity_filtering:
dJ, dvc = applySensitivityFilter(ft, rho, dJ, dvc)
J, dJ = J, dJ.reshape(-1)[:, None]
vc, dvc = vc[:, None], dvc.reshape(dvc.shape[0], -1)
print(f"J.shape = {J.shape}")
print(f"dJ.shape = {dJ.shape}")
print(f"vc.shape = {vc.shape}")
print(f"dvc.shape = {dvc.shape}")
print(f"rho_ini.shape = {rho_ini.shape}")
print(f"rho_physical.shape = {rho_physical.shape}")
exit()
J, dJ, vc, dvc = np.array(J), np.array(dJ), np.array(vc), np.array(dvc)
start = time.time()
mma.setObjectiveWithGradient(J, dJ)
mma.setConstraintWithGradient(vc, dvc)
mma.mmasub(xval)
xmma, _, _ = mma.getOptimalValues()
xold2 = xold1.copy()
xold1 = xval.copy()
xval = xmma.copy()
mma.registerMMAIter(xval, xold1, xold2)
rho = xval.reshape(rho.shape)
end = time.time()
time_elapsed = end - start
print(f"MMA took {time_elapsed} [s]")
print(f'Iter {loop:d}; J {J:.5f}; constraint {vc}\n\n\n')
return rho
