/* From: "COMPUTATIONAL PHYSICS, 2nd Ed" 
   by RH Landau, MJ Paez, and CC Bordeianu 
   Copyright Wiley-VCH, 2007.
   Electronic Materials copyright: R Landau, Oregon State Univ, 2007;
   MJ Paez, Univ Antioquia, 2007; & CC Bordeianu, Univ Bucharest, 2007
   Support by National Science Foundation
*/
// lineq.c: Solve matrix equation Ax = b using LAPACK routine sgesv  
// LAPACK has to be installed on your system   

#include<stdio.h>
#define size 3                                 // dimension of matrix

main()  {
	
  int i, j , c1, c2, pivot[size], ok;
  float A[size][size], b[size], AT[size*size];
	
  A[0][0]= 3.1; A[0][1]=  1.3; A[0][2]= -5.7;             // matrix A
  A[1][0]= 1.0; A[1][1]= -6.9; A[1][2]=  5.8;        
  A[2][0]= 3.4; A[2][1]=  7.2; A[2][2]= -8.8;       
  b[0]= -1.3;                                             // vector b
  b[1]= -0.1;
  b[2]=  1.8;
	                                    // Transform matrix for Fortran
  for (i = 0; i<size; i++)           
    {for (j= 0 ; j < size ; j += 1) AT[j + size*i]= A[j][i];} 
  c1 = size;                // define variable so we can pass pointer  
  c2 = 1;                        
  sgesv(&c1, &c2, AT, &c1, pivot, b, &c1, &ok);   
	
// parameters in the order as they appear in the function call: 
// order of matrix A, number of right hand sides (b), matrix A, 
// leading dimension of A, array records pivoting, 
// result vector b on entry, x on exit, leading dimension of b 
// return value = 0 for success 

  if (!ok) for (j = 0; j<size; j++) printf("%e\n", b[j]);  // print x
  else printf("An error occurred\n");
}