====== LAPACK ======

> LAPACK is a library of Fortran subroutines for solving the most commonly occurring problems in numerical linear algebra.

   * See: https://github.com/Reference-LAPACK/lapack

It is important to note that the BLAS functions included in LAPACK (''libblas.so'' and ''liblapack.so'') are //distinct// to those within OpenBLAS. __Do not__ try to swap out OpenBLAS with LAPACK, or vice versa.

LAPACK can be loaded as follows:

<code>
$ module load LAPACK/3.12.0
</code>

This will automatically adjust LD_LIBRARY_PATH to find the compiled libraries. Headers are also available and should be automatically found by any well configured application using ''PKG_CONFIG_PATH''.

**Do not use LAPACK 3.12.1** - as mentioned below, it has an unresolved error when attempting to link compiled binaries.

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===== Building From Source =====

<WRAP round half important>
**Important**

You only need to read this section if you want to compile a version of LAPACK //yourself//. We reccomend you use the pre-installed module in most circumstances.
</WRAP>

Some applications or libraries may need a specific version of LAPACK. The guide below shows how to configure and compile a specific version of LAPACK into your own directory.

Note that we have found that when attempting to link applications against LAPACK **3.12.1** we see missing symbol errors - this appears to have been reported by at least one Linux distribution (ARCH) missing several symbols (see [[https://bbs.archlinux.org/viewtopic.php?id=302494|1]], and [[https://gitlab.archlinux.org/archlinux/packaging/packages/lapack/-/issues/3|2]]) but appears to not have been fixed upstream.

Either use LAPACK 3.12.0, or > 3.12.1, when it is released.

<code lang=bash>
#!/bin/bash

LAPACK_DIR=$HOME/lapack

echo "Download Lapack ..."
echo "==================="
wget -q https://github.com/Reference-LAPACK/lapack/archive/refs/tags/v3.12.0.tar.gz -O 3.2.0.tgz

echo ""
echo "Untar ..."
echo "========="
tar -zxf 3.2.0.tgz

echo ""
echo "Load modules ..."
echo "================"
module purge
module load GCC/13.3.0

echo ""
echo "Configure ..."
echo "============="
cd lapack-3.12.0
rm -rf build
mkdir build
cd build
CFLAGS="-O3 -pipe -march=znver5"
cmake .. -DBUILD_SHARED_LIBS=ON -DCMAKE_INSTALL_PREFIX=$LAPACK_DIR

echo ""
echo "Compile ..."
echo "==========="
make -j2

echo ""
echo "Install ..."
make install
</code>

To compile code using this specific version of LAPACK you will need to point to the files at ''$HOME/lapack/lib64''. Most users will not need to install LAPACK from source, but this quick guide is for those that do.

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