The support of log double

Barry Smith bsmith at
Mon Dec 4 19:51:20 CST 2006


   You can compile PETSc to use long double with the additional
configure/ options --with-precision=longdouble 

  It compiles a special version of Blas/Lapack for long double.

  I'm not sure this is really the best way to go.

  I would suggest investigating further why intel compiler
works but not gcc. most likely it indicates some error or
memory overwrite in your code. It is also possible that gcc 
generates some incorrect code, does gcc not work even with the
debug version of PETSc? When you run the gcc and intel versions
do they start out pretty much the same and then start diverging
from each other, or are they different straight from the start.
Run with -snes_monitor -ksp_monitor


On Tue, 5 Dec 2006, Gong Ding wrote:

> Hi,
>   I found that PETSC supports long double type
> float point number, which may be useful in my
> semiconductor simulation code.
>   But as i know, no long double support exists in
> BLAS/LAPACK. So can any one tell me the truth
> about long double. 
>   Another problem about SNES is my code diverged 
> with gcc, but works well with Intel icc. Does any
> one meet the same problem? As a result, I 'd like
> to try long double, which seems more accurate to
> double.
> Thanks
> G.D.
> --
> USTC Alumni Email System 

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