[Octave-bug-tracker] [bug #46103] inversion of a singular diagonal matrix A produces inv(A)==A

[Rik]

Update of bug #46103 (project octave):

                  Status:                    None => Need Info              

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Follow-up Comment #5:

For something simple like 2+2 there is a very well-defined output.  For
something more complex like the inverse of a singular matrix there are several
possibilities and arguments can be made for each one.  I am advocating
following the Principle of Least Surprise.  The implementation of diagonal
matrices is optimized in Octave, but users don't need to know or understand
that.  To them, a diagonal matrix is the same as a regular matrix and the same
calculation should yield the same result irrespective of what Octave has used
for the underlying object type.

One useful test is to have the following code run under Matlab


inv (diag (0:2))


If this produces a 3x3 matrix of Inf values then that is what Octave should
also produce.

I can't tell from comment #3 which is considered the odd behavior: 1)
returning the original matrix, or 2) returning an all Inf matrix.  I certainly
want to stop using method 1.  And for the next question, I would prefer to
return Inf (3,3) rather than diag (Inf (3, 1))

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  <http://savannah.gnu.org/bugs/?46103>

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