Matrix Allocation

[Andrew Colombi]

I am a little confused by some behavior.

I've been trying to understand some poor performance numbers and I
noticed that if I doubled the preallocation numbers (presently I'm
setting d_nz and o_nz to constants, no effort has been made to get the
numbers _right_) performance improved dramatically (about 20X).

This isn't so surprising except for the report from MatGetInfo.  Even
with the lower preallocation numbers I'm getting 0 in info.mallocs for

MatInfo info;
MatGetInfo(pc_A, MAT_LOCAL, &info); // done and reported on each
machine individually

So, my question is.... well.. why?  If I'm seeing 0 mallocs before
doubling prealloation shouldn't that mean I've preallocated enough?
Or are their some switches I need to use to enable malloc counting?
Also you can see (according to the same call to MetGetInfo) I'm
wasting a lot of memory:

// after doubling preallocation
nz_alloc 6.2704e+07 nz_used 1.9125e+07 nz_unneed 4.3579e+07

(these are print outs of info.nz_allocated, info.nz_used and info.nzunneeded).

Any thoughts?  For now memory is not a bottleneck, so I guess I'll be
satisfied with guessing big numbers for d_nz and o_nz.  Still, I spent
a lot of time scratching my head since guessing higher numbers didn't
seem likely to have an effect.

Thanks,
-Andrew