//	Ex514.cc

//	Sec. 5.1 of lecture
//	2D arrays
//	Multiplication Matrix*Vector  f := A * u  
//		with A as 2D array   or  B as 1D array

#include <iostream.h>

main()
{
 const int NROW=4, MCOL=3;
 double f[NROW], 
 	a[NROW][MCOL] = {4,-1,-0.5, -1,4,-1, -0.5,-1,4, 3,0,-1 }, 
 	b[NROW*MCOL]  = {4,-1,-0.5, -1,4,-1, -0.5,-1,4, 3,0,-1 }, 
	u[MCOL] = {1,2,3};
 int    i,j;

//		matrix times vector : f := A * u
 for (i=0; i<NROW; i++)
  {
    f[i] = 0.0;			// initialize f[i]
    for (j=0; j<MCOL; j++)
     {
       f[i] = f[i] + a[i][j] * u[j];
     }
  }
//			output result
 cout << endl;
 for (i=0; i<NROW; i++)
  {
   cout << "  " << f[i];
  }
 cout << endl << endl;

//---------------------------------------------------------------

//		matrix times vector : f := B * u
 for (i=0; i<NROW; i++)
  {
    f[i] = 0.0;			// initialize f[i]
    for (j=0; j<MCOL; j++)
     {
       f[i] = f[i] + b[i*MCOL+j] * u[j];
     }
  }
//			output result
 cout << endl;
 for (i=0; i<NROW; i++)
  {
   cout << "  " << f[i];
  }
 cout << endl << endl;
}