On Wed, 13 Nov 2024, Roger Heflin wrote:
On Wed, Nov 13, 2024 at 4:25?PM Patrick Dupre <pdupre@xxxxxxx> wrote:
How different are the values? How many significant figures match? 0? 5?
relatve difference: 2.7e-8
"noise" ~ 1e-35
values < 2e-23
What significant figure is it of the result? Heavy calculations are
sensitive to the precision of the underlying cpu calculations and one
cpu may pick a different underlying precision to use internally. Ie
Not if both CPUs are supposed to be using IEEE 64-bit floating point.
The 80-bit double extended registers go mostly unused lately.
Their use in double precision arithmetic is supposed to be discoverable:
sizeof(double) != sizeof(double_t)
if one machine takes say 3 clock cycles to do a single or a double
then you might as well use a double internally and if the other
machine takes say 3 for a single and 6 for a double then on that
machine the compiler optimization will choose the single (to be
faster) and both may produce a different answer.
Not if both CPUs are supposed to be using IEEE 32-bit floating point.
Again, discoverable: sizeof(float) != sizeof(float_t).
If rounding is indeed the issue,
'tis most likely in the libraries, e.g.,
one evaluates (x+y)+z and the other (x+z)+y .
One might use exp(x)-1 and the other expm1(x) or expl(x)-1 .
OP might swap libraries to test the hypothesis.
--
Michael hennebry@xxxxxxxxxxxxxxxxxxxxxx
"SCSI is NOT magic. There are *fundamental technical
reasons* why it is necessary to sacrifice a young
goat to your SCSI chain now and then." -- John Woods
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