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Large Linear Algebra

hvwahl
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6 years 2 months ago #391 by hvwahl

Large Linear Algebra was created by hvwahl

Hi,

I am trying to compute the eigenvalues of an NGSolve matrix originating from a bilinear form B. My attempt has been to follow the documentation and to create an numpy array using B.mat.NumPy() and B.NumPy(). However this gives me the error message

AttributeError: 'ngsolve.la.SparseMatrixd' object has no attribute 'NumPy'

and

AttributeError: 'ngsolve.comp.BilinearForm' object has no attribute 'NumPy'

respectively.

How can I create a numpy array using NGS-Py so that I work with the matrix using numpy?

Best Wishes,
Henry

Attachments:

..._2018-02-23.py

cwinters
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6 years 2 months ago #392 by cwinters

Replied by cwinters on topic Large Linear Algebra

Hi Henry,

you should follow this reference .
Getting a scipy matrix and calculating the eigenvalues can be done with the following lines.

Code:

import scipy.sparse as sp
from scipy.linalg import eig
rows,cols,vals = B.mat.COO()
M = sp.csr_matrix((array(vals),(array(rows),array(cols))))
# M = sp.csr_matrix((vals,(rows,cols)))
lam = eig(M.todense())

If your version of scipy is not new enough (like in my case 0.17.0) you have to cast the output of COO() to a python array.

Best,
Christoph

The following user(s) said Thank You: hvwahl