[mjcohen]

Back in the 80's, I was programming in Fortran on a VAX 780. I had converted a complex eigenvalue-eigenvector routine from Algol to Fortran, and, after verifying that it worked, decided to see how much bounds checking added to the runtime. I figured since so much array referencing was done that this would be a worst case scenario. In that particular situation, it added about 30%. I decided that this was well worth it and kept array bounds checking on in all my code.

[moloch-hai]

That is pretty silly. Your eigen library had in it everything it needed to ensure its own safety, so anything more just added slowness.

A check performed in a library, or a condition ensured in a library, is wholly as good as the same work done in the compiler. Compilers are not magic, they are just programs.