ARCHITECTURE/OS and round-offs

subhra

I was using the cyclic reduction procedure for inverting directly( without iterations) the block-triagonal matrix arising out of a Poisson Equation.

I found the results to the same code are slightly different on my desktop PC running Windows NT and and on a somewhat DATED cluster of 3 UNIX-machines running Sun's Solaris... The machines are probably of CRAY make..

My desktop PC gives errors of 10 power -5 whereas the unix machine(s) give a higher error 10 power -4..

I would appreciate any idea or comments on this..

Incidentally, when I use the SUN's porprietory fortran compiler f77 and g77 on the UNIX system, I get identical results for this direct solution method.