## Abstract

The latest version of Chapel (version 1.12.0) includes a LAPACK module. To get started, I compiled Chapel, BLAS, and LAPACK, and I ran the example code shipped with Chapel.1

## Software versions referenced:

• Chapel version 1.12.0
• BLAS version 3.5.0
• LAPACK version 3.5.0
• gcc (including gfortran) version 5.2.0 (installed via Homebrew)
• Xcode version 7.0
• Apple LLVM version 7.0.0

## Motivation

I’ve started the ExotiMO project to write a quantum chemistry code that meets some fairly unique requirements:

• written in Chapel so it has all of the goodness that the language has to offer
• can handle arbitrary numbers and types of exotic particles (e.g. system with one positron, two electrons, and a quantum proton)
• can do Hartree-Fock (HF) energies (at first, but post-HF methods and geometry optimizations are planned)

The project stalled out when I wanted to diagonalize a Hamiltonian, and I foolishly attempted to rewrite portions of BLAS and LAPACK in the Chapel language. So, when the Chapel team released version 1.12.0 with some exciting additions, including a LAPACK module, I was anxious to try it out.

## Getting BLAS, LAPACK, and Chapel

LAPACK will require gfortran and BLAS to compile, and BLAS will require gfortran. gfortran can be gotten easily along with gcc using Homebrew, and they will install to /usr/local/Cellar/gcc/5.2.0/bin (as of this writing) as gcc-5 and gfortran with symlinks in /usr/local/bin. Run brew info gcc to confirm for yourself. When installing gcc with brew (brew install gcc), you may run into a problem with the linking of packages mpfr, gmp, and libmpc. This is easily solved with the following commands:

Both BLAS and LAPACK use make.inc files for system-specific configurations. The only thing you might want to change in the BLAS make.inc that is already in the root directory of the distribution is the PLAT variable to append an identifier to the library filename. (I used _DARWIN.) Then just run make, and you will have a blas_DARWIN.a file.

For the LAPACK make.inc file, I copied the file from INSTALL/make.inc.gfortran, and only two changes were necessary. Since I’m using the gfortran from Homebrew, I pointed CC to the gcc from there, too (CC = gcc-5). Also, you want to make sure you are using the BLAS that you just compiled by pointing BLASLIB to the appropriate file. (In my case, BLASLIB = \$(HOME)/BLAS/blas_DARWIN.a.) The Chapel LAPACK module actually uses LAPACKE, the C interface to LAPACK, so the command to compile is actually make lapackelib. You can check the LAPACKE install by running the example shipped with the code (by running make lapacke_example).

(Updated 17 Jan 2016)Although tThe Chapel install page mentions Homebrew as an option for installing a single-locale (shared memory) build of Chapel. Since I am attempting it on the same day as the 1.12.0 release and there is some lag on the order of 24 hours for the Homebrew formulas to be updated, my Homebrew would install version 1.11.0, not the latest one with the LAPACK module. When installing Chapel from source, I’ve initially decided to use the default options in the Makefile using the Apple LLVM compiler that ships with Xcode command-line tools.

## Running the example

Chapel ships with an example program (located at examples/primers/LAPACKlib.chpl) that uses the LAPACK gesv procedure to solve $A \times X = B$ for $X$ given both $A$ and $B$, where $A$ is a square matrix. It also includes a little bit of verification and validation by

• computing $B$ from random $A$ and $X$ matrices before passing $A$ and $B$ to gesv
• comparing the computed $X$ matrix from gesv to the $X$ matrix that was previously generated

A minimal Makefile to compile LAPACKlib.chpl looks something like this:

Success looks something like this:

1. This is not meant to be step-by-step instructions. I don’t outline every step in detail, and I assume the reader has previously compiled and used Chapel on his system and already has things like Homebrew and the Xcode command-line tools.