User guide

NumPy User Guide, Release 1.9.0

FORTRAN ABI mismatch

The two most popular open source fortran compilers are g77 and gfortran. Unfortunately, they are not ABI compatible,

which means that concretely you should avoid mixing libraries built with one with another. In particular, if your

blas/lapack/atlas is built with g77, you must use g77 when building numpy and scipy; on the contrary, if your atlas

is built with gfortran, you must build numpy/scipy with gfortran. This applies for most other cases where different

FORTRAN compilers might have been used.

Choosing the fortran compiler

To build with g77:

python setup.py build --fcompiler=gnu

To build with gfortran:

python setup.py build --fcompiler=gnu95

For more information see:

python setup.py build --help-fcompiler

How to check the ABI of blas/lapack/atlas

One relatively simple and reliable way to check for the compiler used to build a library is to use ldd on the library. If

libg2c.so is a dependency, this means that g77 has been used. If libgfortran.so is a a dependency, gfortran has been

used. If both are dependencies, this means both have been used, which is almost always a very bad idea.

Disabling ATLAS and other accelerated libraries

Usage of ATLAS and other accelerated libraries in Numpy can be disabled via:

BLAS=None LAPACK=None ATLAS=None python setup.py build

Supplying additional compiler ﬂags

Additional compiler ﬂags can be supplied by setting the OPT, FOPT (for Fortran), and CC environment variables.

Building with ATLAS support

Ubuntu 8.10 (Intrepid) and 9.04 (Jaunty)

You can install the necessary packages for optimized ATLAS with this command:

sudo apt-get install libatlas-base-dev

If you have a recent CPU with SIMD suppport (SSE, SSE2, etc...), you should also install the corresponding package

for optimal performances. For example, for SSE2:

sudo apt-get install libatlas3gf-sse2

This package is not available on amd64 platforms.

NOTE: Ubuntu changed its default fortran compiler from g77 in Hardy to gfortran in Intrepid. If you are building

ATLAS from source and are upgrading from Hardy to Intrepid or later versions, you should rebuild everything from

scratch, including lapack.

6 Chapter 1. Introduction