Sina's Blog

CS and AI

1 min readProgramming

Write a Solver for Systems of Equations Using LAPACK on Mac OS

Apple provides the Accelerate library which includes the linear algebra library (LAPACK). In this post, we will go through writing a simple C++ program to use this library on Mac OS.

The Equations

Let’s solve the following equations:

2x0+x1=0x0−x1=0

We can rewrite the equations as:

(211−1)X=(00)

The Code

Now, let’s write our code:

#include <iostream>
#include <Accelerate/Accelerate.h>

int main()
{
    int number_of_rows = 2;
    int number_of_cols = 2;
    int number_of_right_hand_side_cols = 1;
    int LDA = 2;
    int LDB = 2;
    int IPIV[3];
    int INFO = 10;
    char TRANS = 'N'; // Non transpose

    double a[2*2] = {2, 1,
                     1, -1};
    double b[2] = {0,
                   0};

    dgetrf_(&number_of_rows, &number_of_cols, a, &LDA, IPIV, &INFO);
    if (!INFO)
        std::cout << "LU factorization executed without errors." << std::endl;

    dgetrs_(&TRANS, &number_of_rows, &number_of_right_hand_side_cols,
            a, &LDA, IPIV, b, &LDB, &INFO);

    std::cout << "Result: x_0 = " << *b << ", x_1 = " << *(b+1) << std::endl;

    if (!INFO)
        std::cout << "Solver executed without errors." << std::endl;

    return(0);
}

Compile and Run

Now, run the code by using the following commands in a terminal:

#!/bin/bash

g++ -llapack lapack_test.cpp -o ltest.o
./ltest.o
Related posts