#include <stdlib.h>
int strmv(
  const long n,
  const long p,
  const double alpha,
  double **U,    /* two-dimensional array, row-major */
  double **W,    /* two-dimensional array, row-major */
  double *x,     /* one-dimensional array */
  double *ws     /* workspace (length p array) */
  ){

  /*Check if input constants n,p are 0 or pointers are equal to NULL*/
  if ( (n == 0) || (p == 0) || (U == NULL) ||
    (W == NULL) || (x == NULL) || (ws == NULL) ) return -1;

  /*Initialise new double x_new so we don't have to overwrite x in the loop*/
  double x_new = 0;

  for(int i=0; i<n; i++){
    for(int j=0; j<p; j++){
        ws[j] += x[i]*W[i][j];
        x_new += U[i][j]*ws[j];
    }

    /*Update x[i] when out of inner loop and reinitialise x_new*/
    x[i] = alpha*x_new;
    x_new = 0;
  }
  return 0;
}