BLAS and LAPACK#
Default behavior for BLAS and LAPACK selection#
When a NumPy build is invoked, BLAS and LAPACK library detection happens
automatically. The build system will attempt to locate a suitable library,
and try a number of known libraries in a certain order - most to least
performant. A typical order is: MKL, Accelerate, OpenBLAS, FlexiBLAS, BLIS,
plain libblas/liblapack. This may vary per platform or over releases.
That order, and which libraries are tried, can be changed through the
blas-order and lapack-order build options, for example:
$ python -m pip install . -Csetup-args=-Dblas-order=openblas,mkl,blis -Csetup-args=-Dlapack-order=openblas,mkl,lapack
The first suitable library that is found will be used. In case no suitable
library is found, the NumPy build will print a warning and then use (slow!)
NumPy-internal fallback routines. In order to disallow use of those slow routines,
the allow-noblas build option can be used:
$ python -m pip install . -Csetup-args=-Dallow-noblas=false
By default the LP64 (32-bit integer) interface to BLAS and LAPACK will be used.
For building against the ILP64 (64-bit integer) interface, one must use the
use-ilp64 build option:
$ python -m pip install . -Csetup-args=-Duse-ilp64=true
Selecting specific BLAS and LAPACK libraries#
The blas and lapack build options are set to “auto” by default, which
means trying all known libraries. If you want to use a specific library, you
can set these build options to the library name (typically the lower-case name
that pkg-config expects). For example, to select plain libblas and
liblapack (this is typically Netlib BLAS/LAPACK on Linux distros, and can
be dynamically switched between implementations on conda-forge), use:
$ # for a development build
$ spin build -C-Dblas=blas -C-Dlapack=lapack
$ # to build and install a wheel
$ python -m build -Csetup-args=-Dblas=blas -Csetup-args=-Dlapack=lapack
$ pip install dist/numpy*.whl
$ # Or, with pip>=23.1, this works too:
$ python -m pip install . -Csetup-args=-Dblas=blas -Csetup-args=-Dlapack=lapack
Other options that should work (as long as they’re installed with
pkg-config support; otherwise they may still be detected but things are
inherently more fragile) include openblas, mkl, accelerate,
atlas and blis.
Using pkg-config to detect libraries in a nonstandard location#
The way BLAS and LAPACK detection works under the hood is that Meson tries
to discover the specified libraries first with pkg-config, and then
with CMake. If all you have is a standalone shared library file (e.g.,
armpl_lp64.so in /a/random/path/lib/ and a corresponding header
file in /a/random/path/include/), then what you have to do is craft
your own pkg-config file. It should have a matching name (so in this
example, armpl_lp64.pc) and may be located anywhere. The
PKG_CONFIG_PATH environment variable should be set to point to the
location of the .pc file. The contents of that file should be:
libdir=/path/to/library-dir # e.g., /a/random/path/lib
includedir=/path/to/include-dir # e.g., /a/random/path/include
version=1.2.3 # set to actual version
extralib=-lm -lpthread -lgfortran # if needed, the flags to link in dependencies
Name: armpl_lp64
Description: ArmPL - Arm Performance Libraries
Version: ${version}
Libs: -L${libdir} -larmpl_lp64 # linker flags
Libs.private: ${extralib}
Cflags: -I${includedir}
To check that this works as expected, you should be able to run:
$ pkg-config --libs armpl_lp64
-L/path/to/library-dir -larmpl_lp64
$ pkg-config --cflags armpl_lp64
-I/path/to/include-dir