[Octave-bug-tracker] [bug #29786] Octave does not save sparse matrices correctly in -mat format

[Rik]

Update of bug #29786 (project octave):

                  Status:                    None => Confirmed              
                 Summary: Data file can not be loaded in Octave => Octave
does not save sparse matrices correctly in -mat format

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Follow-up Comment #2:

Apparently Octave has trouble saving sparse matrices and has for quite a
while.

I spent some time narrowing the problem down.  The following code is
sufficient to provoke an error.

a = sparse(1,1);
a(1,1) = 1;
b = 2;
save -mat test.mat
clear
load test.mat

The error is reproducible with the current development sources as well as an
ancient 3.0.5 version I tried.

During the load the error message is:
error: load: invalid element type = 1016

I suspect that binary structures are not being properly aligned during the
save process.  For instance, if the variables are reversed so that the sparse
matrix is called b and the double variable is a then everything works.  This
puts the sparse matrix at the end of the file where it can't collide with any
following variables.  Similarly, if the sparse matrix is empty the test
passes.  

These results were obtained on an x86_64 machine.  The original reporter
didn't note whether they were using a 64 bit machine but it could be something
as simple as using an int value and expecting that to be a defined size rather
than using named sizes such as int32_t.

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