John Travers <[email protected]> writes: > Thanks for this. It wasn't obvious to me. I recompiled and get much > better performance.
Great. > OK, this solved my problem. Although I couldn't add zeros on the > diagonal (the software I use to write the sparse matrices optimises > this out), so I put a diagonal of 1e-300. Do you think this will cause > inaccuracies in the calculations (so far it seems OK). Anything at least 1e-16 smaller than the other entries is essentially 0.0 as far as floating point arithmetic is concerned. One possible concern with 1e-300 is creating floating point exceptions due to denormals. For example, if you get a NaN and then turn on trapping FP exceptions (-fp_trap in PETSc) and try to debug, you might get a false positive when the 1e-300 creates a denormal.
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