typedef struct _grid {

  int nrows, ncols;   //the size of  the grid 
  float ** data; // the 2D array of values in the grid 

} Grid; 


/* asume grid is a valid grid with its 2D array allocated. set the
   value of grid.data[i][j] to val*/ 
void set(Grid * g, int i, int j,  float val); 

/* assume grid is a valid grid with data allocated. return the value
   in the grid at position i,j */
float get(Grid g, int i, int j);