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maroba / findiff

Python package for numerical derivatives and partial differential equations in any number of dimensions.
MIT License
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Cannot get matrix representation of irregular spaced operator #21

Closed juliusbierk closed 4 years ago

juliusbierk commented 4 years ago

First of all, thanks for a great library!

An example of the problem I'm having:

from findiff import FinDiff
import numpy as np

x = np.logspace(0, 2, 100)
operator = FinDiff(0, x)
f_test = x**2

assert np.max(np.abs((operator(f_test) - 2*x))) < 1e-12  # Works fine

m_op = operator.matrix(x.shape)  # fails

Traceback:

Traceback (most recent call last):
  File "/home/julius/.PyCharm2019.3/config/scratches/SH.py", line 10, in <module>
    m_op = operator.matrix(x.shape)
  File "/usr/local/lib/python3.6/dist-packages/findiff/operators.py", line 106, in matrix
    return self.pds.matrix(shape, h, acc)
  File "/usr/local/lib/python3.6/dist-packages/findiff/diff.py", line 415, in matrix
    v = c / h**order
TypeError: unsupported operand type(s) for ** or pow(): 'NoneType' and 'int'a

In principle there should be no reason to give the shape of x, since this is internally known, however, calling operator.matrix() throws missing argument exception.

maroba commented 4 years ago

Currently the matrix representation is only supported for uniform grids. The exception is thrown because for nonuniform grids h is None. I will fix that to make sure that this gives a reasonable error message and for the next release I'll try to work on the matrix representation for non-uniform grids. Thanks for reporting this error!