MATLAB Application Program Interface Reference

Set new imaginary data for an mxArray

#include "matrix.h"
void mxSetPi(mxArray *array_ptr, double *pi);

Arguments

array_ptr

Pointer to a full (nonsparse) mxArray.

Pointer to the first element of an array. Each element in the array contains the imaginary component of a value. The array must be in dynamic memory; call mxCalloc to allocate this dynamic memory. If pi points to static memory, memory leaks and other memory errors may result.

Description

Use mxSetPi to set the imaginary data of the specified mxArray.

Most mxCreate functions optionally allocate heap space to hold imaginary data. If you tell an mxCreate function to allocate heap space (for example, by setting the ComplexFlag to mxComplex or by setting pi to a non-NULL value), then you do not ordinarily use mxSetPi to initialize the created mxArray's imaginary elements. Rather, you typically call mxSetPi to replace the initial imaginary values with new ones.

Examples

Create a 1-by-5 mxArray. Then, grow the mxArray to 1-by-6, seeding it with the five elements of the 1-by-5 mxArray.

mxArray  *array_ptr;
  double    start_pr[5] = {3.2, 4.6, 5.1, 6.8, 7.3};
  double    start_pi[5] = {4.5, 4.2, 4.4, 4.8, 4.6};
  double   *new_heap_pr, *new_heap_pi, *pr, *pi; 

/* Create a 1-by-5 complex array of doubles. */ 
  array_ptr = mxCreateDoubleMatrix(1, 5, mxCOMPLEX);
  pr = mxGetPr(array_ptr);
  pi = mxGetPi(array_ptr);
  memcpy((void *)pr,(const void *)start_pr,5*sizeof(double));
  memcpy((void *)pi,(const void *)start_pi,5*sizeof(double));
  mxSetName(array_ptr, "Apricots");
...

/* Add a sixth element to Apricots. */ 

 /* First, allocate heap to hold six complex elements. */ 
   new_heap_pr = (double *)mxCalloc(6, sizeof(double)); 
   new_heap_pi = (double *)mxCalloc(6, sizeof(double)); 

 /* Next, copy the old five complex elements to a new section. */
   memcpy(new_heap_pr, start_pr, 5*sizeof(double));
   memcpy(new_heap_pi, start_pi, 5*sizeof(double));
 
 /* Next, assign the 6th complex element. */
   new_heap_pr[5] = 8.9;
   new_heap_pi[5] = 4.7;
 
 /* Next, free the heap required to hold the old pr and pi. */ 
   mxFree(mxGetPr(array_ptr));
   mxFree(mxGetPi(array_ptr));

 /* Now, change Apricot's dimensions to 1-by-6. */ 
   mxSetN(array_ptr, 6);
 
 /* Finally, associate the new numbers with Apricots. */
   mxSetPr(array_ptr, new_heap_pr);
   mxSetPi(array_ptr, new_heap_pi);

For an additional example, see mxSetPi.c in the mx subdirectory of the examples directory.