#include <iostream>
#include <armadillo>

using namespace std;
using namespace arma;

/* Program to solve 
 * 
 * | 1 4 0 0 | | x1 |    | 8 |
 * | 3 4 1 0 | | x2 | =  | 4 |
 * | 0 2 3 4 | | x3 |    | 2 |
 * | 0 0 1 3 | | x4 |    | 4 |
 * 
 * using armadillo library. To compile on cobra do 
 *
 * g++ tridiag.cc -larmadillo 
 *
 */


int main(int argc, char** argv)
  {
  mat A = zeros<mat>(4,4);
  vec b = zeros<vec>(4);
  vec x = zeros<vec>(4);

  vec::iterator vec_begin = x.begin();
  vec::iterator vec_end = x.end();

  A(0,0)=1.0; A(0,1)=4.0;
  A(1,0)=3.0; A(1,1)=4.0; A(1,2)=1.0;
  A(2,1)=2.0; A(2,2)=3.0; A(2,3)=4.0;
  A(3,2)=1.0; A(3,3)=3.0;

  b(0) = 8.0; b(1)=4.0; b(2)=2.0; b(3)=4.0;

  x = solve(A, b);

  for (vec::iterator i=vec_begin; i!=vec_end; i++ ) {
      cout << *i  << endl;
      }

  return 0;
}