Python Inverse of a Matrix

Question

How do I get the inverse of a matrix in python? I\'ve implemented it myself, but it\'s pure python, and I suspect there are faster modules out there to do it.

Answer 1

It is a pity that the chosen matrix, repeated here again, is either singular or badly conditioned:

A = matrix( [[1,2,3],[11,12,13],[21,22,23]])

By definition, the inverse of A when multiplied by the matrix A itself must give a unit matrix. The A chosen in the much praised explanation does not do that. In fact just looking at the inverse gives a clue that the inversion did not work correctly. Look at the magnitude of the individual terms - they are very, very big compared with the terms of the original A matrix...

It is remarkable that the humans when picking an example of a matrix so often manage to pick a singular matrix!

I did have a problem with the solution, so looked into it further. On the ubuntu-kubuntu platform, the debian package numpy does not have the matrix and the linalg sub-packages, so in addition to import of numpy, scipy needs to be imported also.

If the diagonal terms of A are multiplied by a large enough factor, say 2, the matrix will most likely cease to be singular or near singular. So

A = matrix( [[2,2,3],[11,24,13],[21,22,46]])

becomes neither singular nor nearly singular and the example gives meaningful results... When dealing with floating numbers one must be watchful for the effects of inavoidable round off errors.

Thanks for your contribution,

OldAl.