pymor.algorithms.symplectic

Module Contents

class pymor.algorithms.symplectic.SymplecticBasis(E=None, F=None, phase_space=None, check_symplecticity=True)

Bases: pymor.core.base.BasicObject

A canonically-symplectic basis based on pairs of basis vectors (e_i, f_i).

Is either initialized (a) with a pair of VectorArrays E and F or (b) with a VectorSpace. The basis vectors are each contained in a VectorArray

E = (e_i)_{i=1}^n F = (f_i)_{i=1}^n

such that

V = [E, F].

Parameters

E

A VectorArray that represents the first half of basis vectors. May be none if phase_space is specified.

F

A VectorArray that represents the second half of basis vectors. May be none if phase_space is specified.

phase_space

A VectorSpace that represents the phase space. May be none if E and F are specified.

check_symplecticity

Flag, whether to check symplecticity of E and F in the constructor (if these are not None). Default is True.

Methods

append	Append another SymplecticBasis.
extend	Extend the SymplecticBasis with vectors from a VectorArray.
from_array	Generate SymplecticBasis from VectorArray.
lincomb
to_array	Convert to VectorArray.
transposed_symplectic_inverse	Compute transposed symplectic inverse J_{2N}.T * V * J_{2n}.

append(other, remove_from_other=False, check_symplecticity=True)

Append another SymplecticBasis.

other

The SymplecticBasis to append.

remove_from_other

Flag, whether to remove vectors from other.

check_symplecticity

Flag, whether to check symplecticity of E and F in the constructor (if these are not None). Default is True.

extend(U, method='svd_like', modes=2, product=None)

Extend the SymplecticBasis with vectors from a VectorArray.

Parameters

U

The vectors used for the extension as VectorArray.

method

The method used for extension. Available options are

(‘svd_like’, ‘complex_svd’, ‘symplectic_gram_schmidt’).

modes

Number of modes to extract from U. Has to be even.

product

A product to use for the projection error. Default is None.

classmethod from_array(U, check_symplecticity=True)

Generate SymplecticBasis from VectorArray.

Parameters

U

The VectorArray.

check_symplecticity

Flag, whether to check symplecticity of E and F in the constructor (if these are not None). Default is True.

Returns

BASIS

The SymplecticBasis.

lincomb(coefficients)

to_array()

Convert to VectorArray.

Returns

BASIS

The SymplecticBasis as VectorArray.

transposed_symplectic_inverse()

Compute transposed symplectic inverse J_{2N}.T * V * J_{2n}.

Returns

TSI_BASIS

The transposed symplectic inverse as SymplecticBasis.

pymor.algorithms.symplectic.esr(E, F, J=None)

Elementary SR factorization. Transforms E and F such that.

[E, F] = S * diag(r11, r22)

Coefficients are chosen such that ||E|| = ||F||. r12 is set to zero.

Parameters

E

A VectorArray of dim=1 from the same VectorSpace as F.

F

A VectorArray of dim=1 from the same VectorSpace as E.

J

A CanonicalSymplecticFormOperator operating on the same VectorSpace as E and F. Default is CanonicalSymplecticFormOperator(E.space).

Returns

R

A diagonal numpy.ndarray.

pymor.algorithms.symplectic.psd_complex_svd(U, modes)

Generates a SymplecticBasis with the PSD complex SVD.

This is an implementation of Algorithm 2 in [PM16].

Parameters

U

The VectorArray for which the PSD SVD-like decomposition is to be computed.

modes

Number of modes (needs to be even).

Returns

BASIS

The SymplecticBasis.

pymor.algorithms.symplectic.psd_cotangent_lift(U, modes)

Generates a SymplecticBasis with the PSD cotangent lift.

This is an implementation of Algorithm 1 in [PM16].

Parameters

U

The VectorArray for which the PSD SVD-like decomposition is to be computed.

modes

Number of modes (needs to be even).

Returns

BASIS

The SymplecticBasis.

pymor.algorithms.symplectic.psd_svd_like_decomp(U, modes, balance=True)

Generates a SymplecticBasis with the PSD SVD-like decomposition.

This is an implementation of Algorithm 1 in [BBH19].

Parameters

U

The VectorArray for which the PSD SVD-like decomposition is to be computed.

modes

Number of modes (needs to be even).

balance

A flag, whether to balance the norms of pairs of basis vectors.

Returns

BASIS

The SymplecticBasis.

pymor.algorithms.symplectic.symplectic_gram_schmidt(E, F, return_Lambda=False, atol=1e-13, rtol=1e-13, offset=0, reiterate=True, reiteration_threshold=0.9, check=True, check_tol=0.001, copy=True)

Symplectify a VectorArray using the modified symplectic Gram-Schmidt algorithm.

This is an implementation of Algorithm 3.2. in [AA11] with a modified criterion for reiteration.

Decomposition:

[E, F] = S * Lambda

with S symplectic and Lambda a permuted upper-triangular matrix.

Parameters

E, F

The two VectorArrays which are to be symplectified.

return_Lambda

If True, the matrix Lambda from the decomposition is returned.

atol

Vectors of norm smaller than atol are removed from the array.

rtol

Relative tolerance used to detect non-symplectic subspaces (which are then removed from the array).

offset

Assume that the first offset pairs vectors in E and F are already symplectic and start the algorithm at the offset + 1-th vector.

reiterate

If True, symplectify again if the symplectic product of the symplectified vectors is much smaller than the symplectic product of the original vector.

reiteration_threshold

If reiterate is True, “re-orthonormalize” if the ratio between the symplectic products of the symplectified vectors and the original vectors is smaller than this value.

check

If True, check if the resulting VectorArray is really symplectic.

check_tol

Tolerance for the check.

Returns

S

The symplectified VectorArray.

Lambda

if return_Lambda is True.