32bit vs. 64bit

[Michael D. Godfrey]

>
> RNDr. Jaroslav Hajek  wrote:
> When comparing results on architectures that have guard
> > bits, the
> > results obviously depend on the number of registers, unless
> > you use
> > -ffloat-store.
This and other architecture differences in optimization, etc., can
explain this behavior.  The Fortran coded version (compiled with
gfortran)  also produces a different result for the difference of the 2
vectors. (All the other results, as displayed as floating point output,
match exactly.)

One reason for pointing this out is that Matlab claims "bit exact"
results across supported architectures.  This is at considerable
cost to them, and I think it is not a sensible objective.  In any case,
they can only try to do this because they only ship binaries.

In any case, rounding error analysis  get less attention these days
than it deserves.  Courses in numerical error analysis, even using good old
texts like Wilkinson or Forsythe and Moler, are hardly taught anymore...

Michael