Initializing help system before first use

XSLPsetcbconstruct, XPRSsetcbslpconstruct

Purpose
Set a user callback to be called during the Xpress-SLP augmentation process
Topic areas
Callback, SLP
Synopsis
int XPRS_CC XSLPsetcbconstruct(XSLPprob prob, int (XPRS_CC *construct) (XSLPprob cbprob, void *cbdata), void *data);
Arguments
prob 
The current SLP problem.
construct 
The function to be called during problem augmentation. construct returns an integer value. See below for an explanation of the values.
cbprob 
The problem passed to the callback function.
cbdata 
The user-defined object passed as data to XSLPsetcbconstruct.
data 
Address of a user-defined object, which can be used for any purpose by the function. data is passed to construct as cbdata.
Example
The following example sets up a callback to be executed during the Xpress-SLP problem augmentation: 
double *cValue;
cValue = NULL;
XSLPsetcbconstruct(prob, CBConstruct, &cValue);
The following sample callback function sets values for the variables the first time the function is called and returns to XSLPconstruct to recalculate the initial matrix. The second time it is called it frees the allocated memory and returns to XSLPconstruct to proceed with the rest of the augmentation. 
int XPRS_CC CBConstruct(XSLPprob MyProb, void *Obj) {
  double *cValue;
  int i, n;
/* if data is NULL, this is first-time entry */
  if (*(void**)Obj == NULL) {
    XSLPgetintattrib(MyProb,XPRS_COLS,&n);
    cValue = malloc(n*sizeof(double));
/* ... initialize with values (not shown here) and then ... */
    for (i=0;i<n;i++)
/* store into SLP structures */
      XSLPchgvar(MyProb, i, NULL, NULL, NULL, NULL,
                 NULL, NULL, &cValue[i], NULL, NULL, NULL,
                 NULL);
/* set data non-null to indicate we have processed data */
    *(void**)Obj = cValue;
    return -1;
  }
  else {
/* free memory, clear marker and continue */
    free(*(void**)Obj);
    *(void**)Obj = NULL;
  }
  return 0;
}
Further information
1. This callback can be used during the problem augmentation, generally (although not exclusively) to change the initial values for the variables.
2. The following return codes are accepted:
0
Normal return: augmentation continues
-1
Return to recalculate matrix values
-2
Return to recalculate row weights and matrix entries
other
Error return: augmentation terminates, XSLPconstruct terminates with a nonzero error code.
3. The return values -1 and -2 will cause the callback to be called a second time after the matrix has been recalculated. It is the responsibility of the callback to ensure that it does ultimately exit with a return value of zero.
Related topics
XSLPconstruct

Parent Topic Library functions

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