[Octave-bug-tracker] [bug #39000] Can't override BLAS XERBLA handler on Windows

[John W. Eaton]

Follow-up Comment #37, bug #39000 (project octave):

I guess it depends on what kinds of error messages and results you want from
calls to BLAS and LAPACK functions for bad inputs.

I see a few different categories.

1. Incorrect parameters that shouldn't happen (we screw up a call, for
example).  We still don't want Octave to crash.  So our version of xerbla
should be called and throw an error.

2. Matrix and vector arguments with NaN or Inf values that don't make sense
for functions that we call.  Should we protect calls that we make and return
results?  This is a case-by-case thing.  If we can identify and return
"reasonable" results (NaNs, 0, Inf, whatever) instead of throwing an error, we
probably should.

3. Matrix and vector arguments with NaN or Inf values that don't make sense
for internal functions.  Same as above, if we can prevent the call somehow, we
probably should.  But these will be harder to detect.

Since it's probably impossible to detect all possible cases, we really have to
have our own version of xerbla that doesn't cause Octave to exit.

FWIW, it's clear that the BLAS authors intended for users to replace XERBLA
with their own version.  Back in the day, that was simple because you were
building the library for yourself anyway.  Now it seems absurd that there is
no standard way for a user of the BLAS to provide a replacement for this
function without modifying the library sources.

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