On Wed, Nov 13, 2024 at 4:25 PM Patrick Dupre pdupre@gmx.com 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 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.
And likely NEITHER answer is mathematically exact and/or could even be correct especially if the calculation is done in the wrong order that causes significant sensitivities to underlying precision used by the computer and/or cpu.