[petsc-dev] ugliness due to missing lapack routines

[Barry Smith]

On Feb 6, 2013, at 10:53 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> 
> On Wed, Feb 6, 2013 at 10:45 PM, Matthew Knepley <knepley at gmail.com> wrote:
> I think we have to make a distinction as to what kind of code is in there. The proposed
> stub does nothing but raise an error, just as Fortran stubs do nothing but forward the call.
> To me, this should be kept out of petscblaslapack.h.
> 
> petscblaslapack.h needs to know not to redefine those function names. I'd much rather have
> 
> #if defined(PETSC_MISSING_LAPACK_FOO)
> ... definition that raises an error
> #else
> ... normal definition
> #endif
> 
> than
> 
> #if !defined(PETSC_MISSING_LAPACK_FOO)
> ... normal definition
> /* missing definition is generated */
> #endif

   I disagree (there will be NO mention of PETSC_MISSING_LAPACK_FOO anywhere in PETSc source code) In this case we "fixing" broken LAPACK packages. We should not dirty the PETSc source tree AT all because of broken LAPACK. The PETSc source tree should be clean because it assumes a complete lapack.

  Jed writes 
>  petscblaslapack.h needs to know not to redefine those function names. I'd much rather have

   this is wrong. petscblaslapack.h WILL NOT CHANGE at all. Matt will generate exactly the missing lapack routines with their appropriate names. So for a double precision build with _ on BLAS/LAPACK routines Matt will generate 

    void dgeev_(whatever the args are)
         set info to appropriate error code.

  (Note that BuildSystem already knows all about the mangling so generating this with and without underscore, CAPS etc is easy) Matt will NOT generate LAPACKgeev() or something like that.

  In fact Matt can also generate the appropriate zdot_() when needed so ugly crap like
/* handle complex dot() with special code */
#if defined(PETSC_USE_COMPLEX)
PETSC_STATIC_INLINE PetscScalar BLASdot_(const PetscBLASInt *n,const PetscScalar *x,const PetscBLASInt *sx,const PetscScalar *y,const PetscBLASInt *sy)
{
  PetscScalar sum=0.0;
  PetscInt    i,j,k;
  if (*sx==1 && *sy==1) {
    for (i=0; i < *n; i++) sum += PetscConj(x[i])*y[i];
  } else {
    for (i=0,j=0,k=0; i < *n; i++,j+=*sx,k+=*sy) sum += PetscConj(x[j])*y[k];
  }
  return sum;
}
PETSC_STATIC_INLINE PetscScalar BLASdotu_(const PetscBLASInt *n,const PetscScalar *x,const PetscBLASInt *sx,const PetscScalar *y,const PetscBLASInt *sy)
{
  PetscScalar sum=0.0;
  PetscInt    i,j,k;
  if (*sx==1 && *sy==1) {
    for (i=0; i < *n; i++) sum += x[i]*y[i];
  } else {
    for (i=0,j=0,k=0; i < *n; i++,j+=*sx,k+=*sy) sum += x[j]*y[k];
  }
  return sum;
}
#else
PETSC_EXTERN_C PetscScalar BLASdot_(const PetscBLASInt*,const PetscScalar*,const PetscBLASInt*,const PetscScalar*,const PetscBLASInt*);
PETSC_EXTERN_C PetscScalar BLASdotu_(const PetscBLASInt*,const PetscScalar*,const PetscBLASInt*,const PetscScalar*,const PetscBLASInt*);
#endif

can be removed from the petscblaslapack.h

  Barry



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