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

[Rik]

Follow-up Comment #9, bug #46103 (project octave):

@Mike: Could you try the sparse example under Matlab?


x = sparse (diag ([1 0]))
y = inv (x)


Under Octave it simply refuses to calculate an answer


octave:6> x = sparse (diag ([1 0]))
x =

Compressed Column Sparse (rows = 2, cols = 2, nnz = 1 [25%])

  (1, 1) ->  1

octave:7> y = inv (x)
error: inv: division by zero


This could be another option to use for singular diag matrices.  It would
certainly be easier to implement.  The C++ inverse function defined in
dDiagMatrix.cc returns a DiagMatrix, not an octave_value.  Thus we can't
easily mutate the return value from the special DiagMatrix class to the
ordinary Matrix class.  I suppose one could do so at a higher level in inv.cc
by checking for any element equal to 0.  That's pretty easy check on a
diagonal matrix.



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