Geografic-Information-System/lib/gmath/mult.c

/* Author: Bill Hoff,2-114C,8645,3563478 (hoff) at uicsl */

/*!
 * \fn int mult (double *v1[2], int size1, double *v2[2], int size2, double *v3[2], int size3)
 *
 * \brief Multiply two complex vectors, point by point
 *
 * Vectors are in the form: real, imaginary (each a floating number).  
 * A vector can be of any size. Computes <b>v3</b> = <b>v1</b> * 
 * <b>v2</b>.  <b>v3</b> should as big as the biggest of <b>v1</b> and 
 * <b>v2</b>.
 *
 * \param v1
 * \param size1
 * \param v2
 * \param size2
 * \param v3
 * \param size3
 * \return int
 */

int 
mult (double *v1[2], int size1, double *v2[2], int size2, double *v3[2], int size3)
{
  int i, n;

  n = (size1 < size2 ? size1 : size2); /* get the smaller size */
  for (i=0; i < n; i++) {
    *(v3[0]+i) = *(v1[0]+i) * *(v2[0]+i) - *(v1[1]+i) * *(v2[1]+i);
    *(v3[1]+i) = *(v1[0]+i) * *(v2[1]+i) + *(v2[0]+i) * *(v1[1]+i);
  }

  /* if unequal size, zero out remaining elements of larger vector */
  if (size1 != size2)
    for (i=n; i < size3; i++)   {
      *(v3[0]+i) = 0.0;
      *(v3[1]+i) = 0.0;
    }

  return 0;
}