def reduce(self, r, projection='bfsr'):
"""Reduce using SOBT.
Parameters
----------
r
Order of the reduced model.
projection
Projection method used:
- `'sr'`: square root method
- `'bfsr'`: balancing-free square root method (default, since it avoids scaling by
singular values and orthogonalizes the projection matrices, which might make it more
accurate than the square root method)
- `'biorth'`: like the balancing-free square root method, except it biorthogonalizes the
projection matrices
Returns
-------
rom
Reduced-order |SecondOrderModel|.
"""
assert 0 < r < self.fom.order
assert projection in ('sr', 'bfsr', 'biorth')
# compute all necessary Gramian factors
pcf = self.fom.gramian('pc_lrcf', mu=self.mu)
pof = self.fom.gramian('po_lrcf', mu=self.mu)
vcf = self.fom.gramian('vc_lrcf', mu=self.mu)
vof = self.fom.gramian('vo_lrcf', mu=self.mu)
if r > min(len(pcf), len(pof), len(vcf), len(vof)):
raise ValueError(
'r needs to be smaller than the sizes of Gramian factors.')
# find necessary SVDs
Up, sp, Vp = spla.svd(pof.inner(pcf), lapack_driver='gesvd')
Up = Up.T
Uv, sv, Vv = spla.svd(vof.inner(vcf, product=self.fom.M),
lapack_driver='gesvd')
Uv = Uv.T
# compute projection matrices and find the reduced model
self.V1 = pcf.lincomb(Vp[:r])
self.W1 = pof.lincomb(Up[:r])
self.V2 = vcf.lincomb(Vv[:r])
self.W2 = vof.lincomb(Uv[:r])
if projection == 'sr':
alpha1 = 1 / np.sqrt(sp[:r])
self.V1.scal(alpha1)
self.W1.scal(alpha1)
alpha2 = 1 / np.sqrt(sv[:r])
self.V2.scal(alpha2)
self.W2.scal(alpha2)
W1TV1invW1TV2 = self.W1.inner(self.V2)
projected_ops = {'M': IdentityOperator(NumpyVectorSpace(r))}
elif projection == 'bfsr':
gram_schmidt(self.V1, atol=0, rtol=0, copy=False)
gram_schmidt(self.W1, atol=0, rtol=0, copy=False)
gram_schmidt(self.V2, atol=0, rtol=0, copy=False)
gram_schmidt(self.W2, atol=0, rtol=0, copy=False)
W1TV1invW1TV2 = spla.solve(self.W1.inner(self.V1),
self.W1.inner(self.V2))
projected_ops = {
'M': project(self.fom.M,
range_basis=self.W2,
source_basis=self.V2)
}
elif projection == 'biorth':
gram_schmidt_biorth(self.V1, self.W1, copy=False)
gram_schmidt_biorth(self.V2,
self.W2,
product=self.fom.M,
copy=False)
W1TV1invW1TV2 = self.W1.inner(self.V2)
projected_ops = {'M': IdentityOperator(NumpyVectorSpace(r))}
projected_ops.update({
'E':
project(self.fom.E.assemble(mu=self.mu),
range_basis=self.W2,
source_basis=self.V2),
'K':
project(self.fom.K.assemble(mu=self.mu),
range_basis=self.W2,
source_basis=self.V1.lincomb(W1TV1invW1TV2.T)),
'B':
project(self.fom.B.assemble(mu=self.mu),
range_basis=self.W2,
source_basis=None),
'Cp':
project(self.fom.Cp.assemble(mu=self.mu),
range_basis=None,
source_basis=self.V1.lincomb(W1TV1invW1TV2.T)),
'Cv':
project(self.fom.Cv.assemble(mu=self.mu),
range_basis=None,
source_basis=self.V2),
'D':
self.fom.D.assemble(mu=self.mu),
})
rom = SecondOrderModel(name=self.fom.name + '_reduced',
**projected_ops)
rom.disable_logging()
return rom
def build_rom(self, projected_operators, error_estimator):
return SecondOrderModel(error_estimator=error_estimator, **projected_operators)
def main(
n: int = Argument(
101, help='Order of the full second-order model (odd number).'),
r: int = Argument(5, help='Order of the ROMs.'),
):
"""Parametric string example."""
set_log_levels({'pymor.algorithms.gram_schmidt.gram_schmidt': 'WARNING'})
# Assemble M, D, K, B, C_p
assert n % 2 == 1, 'The order has to be an odd integer.'
n2 = (n + 1) // 2
k = 0.01 # stiffness
M = sps.eye(n, format='csc')
E = sps.eye(n, format='csc')
K = sps.diags(
[n * [2 * k * n**2], (n - 1) * [-k * n**2],
(n - 1) * [-k * n**2]], [0, -1, 1],
format='csc')
B = np.zeros((n, 1))
B[n2 - 1, 0] = n
Cp = np.zeros((1, n))
Cp[0, n2 - 1] = 1
# Second-order system
Mop = NumpyMatrixOperator(M)
Eop = NumpyMatrixOperator(E) * ProjectionParameterFunctional('damping')
Kop = NumpyMatrixOperator(K)
Bop = NumpyMatrixOperator(B)
Cpop = NumpyMatrixOperator(Cp)
so_sys = SecondOrderModel(Mop, Eop, Kop, Bop, Cpop)
print(f'order of the model = {so_sys.order}')
print(f'number of inputs = {so_sys.dim_input}')
print(f'number of outputs = {so_sys.dim_output}')
mu_list = [1, 5, 10]
w = np.logspace(-3, 2, 200)
# System poles
fig, ax = plt.subplots()
for mu in mu_list:
poles = so_sys.poles(mu=mu)
ax.plot(poles.real, poles.imag, '.', label=fr'$\mu = {mu}$')
ax.set_title('System poles')
ax.legend()
plt.show()
# Magnitude plots
fig, ax = plt.subplots()
for mu in mu_list:
so_sys.mag_plot(w, ax=ax, mu=mu, label=fr'$\mu = {mu}$')
ax.set_title('Magnitude plot of the full model')
ax.legend()
plt.show()
# "Hankel" singular values
fig, ax = plt.subplots(2,
2,
figsize=(12, 8),
sharey=True,
constrained_layout=True)
for mu in mu_list:
psv = so_sys.psv(mu=mu)
vsv = so_sys.vsv(mu=mu)
pvsv = so_sys.pvsv(mu=mu)
vpsv = so_sys.vpsv(mu=mu)
ax[0, 0].semilogy(range(1,
len(psv) + 1),
psv,
'.-',
label=fr'$\mu = {mu}$')
ax[0, 1].semilogy(range(1, len(vsv) + 1), vsv, '.-')
ax[1, 0].semilogy(range(1, len(pvsv) + 1), pvsv, '.-')
ax[1, 1].semilogy(range(1, len(vpsv) + 1), vpsv, '.-')
ax[0, 0].set_title('Position singular values')
ax[0, 1].set_title('Velocity singular values')
ax[1, 0].set_title('Position-velocity singular values')
ax[1, 1].set_title('Velocity-position singular values')
fig.legend(loc='upper center', ncol=len(mu_list))
plt.show()
# System norms
for mu in mu_list:
print(f'mu = {mu}:')
print(f' H_2-norm of the full model: {so_sys.h2_norm(mu=mu):e}')
if config.HAVE_SLYCOT:
print(
f' H_inf-norm of the full model: {so_sys.hinf_norm(mu=mu):e}'
)
print(
f' Hankel-norm of the full model: {so_sys.hankel_norm(mu=mu):e}'
)
# Model order reduction
run_mor_method_param(so_sys, r, w, mu_list, SOBTpReductor, 'SOBTp')
run_mor_method_param(so_sys, r, w, mu_list, SOBTvReductor, 'SOBTv')
run_mor_method_param(so_sys, r, w, mu_list, SOBTpvReductor, 'SOBTpv')
run_mor_method_param(so_sys, r, w, mu_list, SOBTvpReductor, 'SOBTvp')
run_mor_method_param(so_sys, r, w, mu_list, SOBTfvReductor, 'SOBTfv')
run_mor_method_param(so_sys, r, w, mu_list, SOBTReductor, 'SOBT')
run_mor_method_param(so_sys, r, w, mu_list, SORIRKAReductor, 'SOR-IRKA')
run_mor_method_param(so_sys.to_lti(), r, w, mu_list, BTReductor, 'BT')
run_mor_method_param(so_sys.to_lti(), r, w, mu_list, IRKAReductor, 'IRKA')