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vander.py
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vander.py
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# Copyright (C) 2018 by the RROMPy authors
#
# This file is part of RROMPy.
#
# RROMPy is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# RROMPy is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with RROMPy. If not, see <http://www.gnu.org/licenses/>.
#
import numpy as np
from rrompy.utilities.poly_fitting.polynomial import polyder
from rrompy.utilities.base.types import Np1D, Np2D, List, paramList
from rrompy.parameter import checkParameterList
from rrompy.utilities.exception_manager import RROMPyException, RROMPyAssert
__all__ = ['polyvander']
def firstDerTransition(dim:int, TDirac:List[Np2D], basis:str,
scl : Np1D = None) -> Np2D:
C_m = np.zeros((dim, len(TDirac), len(TDirac)), dtype = float)
for j, Tj in enumerate(TDirac):
m, om = [0] * dim, [(0, 0)] * dim
for idx in range(dim):
m[idx], om[idx] = 1, (0, 1)
J_der = polyder(Tj, basis, m, scl)
C_m[idx, :, j] = np.ravel(np.pad(J_der, mode = "constant",
pad_width = om))
m[idx], om[idx] = 0, (0, 0)
return C_m
def countDerDirections(n:int, base:int, digits:int, idx:int):
if digits == 0: return []
dig = n % base
return [(idx, dig)] * (dig > 0) + countDerDirections(
(n - dig) // base, base, digits - 1, idx + 1)
def polyvander(x:paramList, degs:List[int], basis:str,
derIdxs : List[List[List[int]]] = None,
reorder : List[int] = None, scl : Np1D = None) -> Np2D:
"""
Compute Hermite-Vandermonde matrix with specified derivative directions.
E.g. assume that we want to obtain the Vandermonde matrix for
(value, derx, derx2) at x = [0, 0],
(value, dery) at x = [1, 0],
(dery, derxy) at x = [0, 0],
of degree 3 in x and 1 in y, using Chebyshev polynomials.
This can be done by
polyvander([[0, 0], [1, 0]], # unique sample points
[3, 1], # polynomial degree
"chebyshev", # polynomial family
[
[[0, 0], [1, 0], [2, 0], [0, 1], [1, 1]],
# derivative directions at first point
[[0, 0], [0, 1]] # derivative directions at second point
],
[0, 1, 2, 5, 6, 3, 4] # reorder indices
)
"""
if not isinstance(degs, (list,tuple,np.ndarray,)): degs = [degs]
dim = len(degs)
x = checkParameterList(x, dim)[0]
x_un, idx_un = x.unique(return_inverse = True)
if len(x_un) < len(x):
raise RROMPyException("Sample points must be distinct.")
del x_un
try:
vanderbase = {"CHEBYSHEV" : np.polynomial.chebyshev.chebvander,
"LEGENDRE" : np.polynomial.legendre.legvander,
"MONOMIAL" : np.polynomial.polynomial.polyvander
}[basis.upper()]
except:
raise RROMPyException("Polynomial basis not recognized.")
VanBase = vanderbase(x(0), degs[0])
for j in range(1, dim):
VNext = vanderbase(x(j), degs[j])
for jj in range(j): VNext = np.expand_dims(VNext, 1)
VanBase = VanBase[..., None] * VNext
VanBase = VanBase.reshape((len(x), -1))
if derIdxs is None or VanBase.shape[-1] <= 1:
Van = VanBase
else:
derFlat, idxRep = [], []
for j, derIdx in enumerate(derIdxs):
derFlat += derIdx[:]
idxRep += [j] * len(derIdx[:])
for j in range(len(derFlat)):
if not hasattr(derFlat[j], "__len__"):
derFlat[j] = [derFlat[j]]
RROMPyAssert(len(derFlat[j]), dim, "Number of dimensions")
TDirac = [y.reshape([d + 1 for d in degs])
for y in np.eye(VanBase.shape[-1], dtype = int)]
Cs_loc = firstDerTransition(dim, TDirac, basis, scl)
Van = np.empty((len(derFlat), VanBase.shape[-1]),
dtype = VanBase.dtype)
for j in range(len(derFlat)):
Van[j, :] = VanBase[idxRep[j], :]
for k in range(dim):
for der in range(derFlat[j][k]):
Van[j, :] = Van[j, :].dot(Cs_loc[k]) / (der + 1)
if reorder is not None: Van = Van[reorder, :]
return Van

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