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# PetscBLASInt

datatype used to represent ‘int’ parameters to BLAS/LAPACK functions.

## Notes

Usually this is the same as `PetscInt`, but if PETSc was built with `--with-64-bit-indices` but standard C/Fortran integers are 32-bit then this may not be the same as `PetscInt`, except on some BLAS/LAPACK implementations that support 64-bit integers see the notes below.

`PetscErrorCode` `PetscBLASIntCast`(a,&b) checks if the given `PetscInt` a will fit in a `PetscBLASInt`, if not it generates a `PETSC_ERR_ARG_OUTOFRANGE` error

Installation Notes: ./configure automatically determines the size of the integers used by BLAS/LAPACK except when `--with-batch` is used in that situation one must know (by some other means) if the integers used by BLAS/LAPACK are 64-bit and if so pass the flag `--known-64-bit-blas-indices`

MATLAB ships with BLAS and LAPACK that use 64-bit integers, for example if you run ./configure with, the option `--with-blaslapack-lib`=[/Applications/MATLAB_R2010b.app/bin/maci64/libmwblas.dylib,/Applications/MATLAB_R2010b.app/bin/maci64/libmwlapack.dylib]

MKL ships with both 32 and 64-bit integer versions of the BLAS and LAPACK. If you pass the flag `-with-64-bit-blas-indices` PETSc will link against the 64-bit version, otherwise it uses the 32-bit version

OpenBLAS can be built to use 64-bit integers. The ./configure options `--download-openblas` `-with-64-bit-blas-indices` will build a 64-bit integer version

External packages such as hypre, ML, SuperLU etc do not provide any support for passing 64-bit integers to BLAS/LAPACK so cannot be used with PETSc when PETSc links against 64-bit integer BLAS/LAPACK. ./configure will generate an error if you attempt to link PETSc against any of these external libraries while using 64-bit integer BLAS/LAPACK.

## See Also

`PetscMPIInt`, `PetscInt`, `PetscBLASIntCast()`

## Level

intermediate

## Location

include/petscsystypes.h

Index of all Sys routines
Table of Contents for all manual pages
Index of all manual pages