Rescaling a general size vector (original) (raw)

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Rescaling a general size vector

Multiplying or dividing a vector by a scalar value follows the scheme of the above copy, addition and subtraction operations. To multiply a vector ${\bf x}$ by a scalar $s$ , ${\bf y}=s{\bf x}$ , use for example

  Gan_Vector vx, vy; /* declare vectors x & y */

  /* ... create & fill vx, create (& optionally fill) vy ... */
  gan_vec_scale_q ( &vx, 5.0, &vy ); /* y = 5*x */

to multiply all the elements in vector ${\bf x}$ by five, writing the result into vector ${\bf y}$ . Alternatively you can create the rescaled vector from scratch as in

  Gan_Vector *pvy; /* declare vector y */

  /* ... create & fill vx ... */
  pvy = gan_vec_scale_s ( &vx, 5.0 ); /* y = 5*x */

or overwrite ${\bf x}$ with the result

  gan_vec_scale_i ( &vx, 5.0 ); /* replace x = 5*x */

There are similar routines for dividing a general size vector by a scalar value:

  gan_vec_divide_q ( &vx, 5.0, &vy ); /* y = x/5 */
  pvy = gan_vec_divide_s ( &vx, 5.0 ); /* y = x/5 */
  gan_vec_divide_i ( &vx, 5.0 ); /* replace x = x/5 */

Passing zero as the scalar value in this case invokes the error handler, with a division by zero error (error code GAN_ERROR_DIVISION_BY_ZERO), and NULL is returned.

There are specific routines to negate a vector, i.e. multiply it by -1, as follows:

  gan_vec_negate_q ( &vx, &vy ); /* y = -x */
  pvy = gan_vec_negate_s ( &vx ); /* y = -x */
  gan_vec_negate_i ( &vx ); /* replace x = -x */

Error detection: The Gandalf error handler is invoked and NULLis returned if an error occurs. The most likely failure modes are (i) failing to create the result vector; (ii) division by zero.

Next: General size matrices Up: General size vectors Previous: General size vector subtraction Contents

2006-03-17