Initializing help system before first use

# XPRSaddcbgapnotify

Purpose
Declares a gap notification callback, to be called when a MIP solve reaches a predefined target, set using the MIPRELGAPNOTIFY, MIPABSGAPNOTIFY, MIPABSGAPNOTIFYOBJ and/or MIPABSGAPNOTIFYBOUND controls.
Topic areas
Callback, Limits
Synopsis
`int XPRS_CC XPRSaddcbgapnotify(XPRSprob prob, void (XPRS_CC *gapnotify)(XPRSprob cbprob, void* cbdata, double* p_relgapnotifytarget, double* p_absgapnotifytarget, double* p_absgapnotifyobjtarget, double* p_absgapnotifyboundtarget), void* data, int priority);`
Arguments

prob | The current problem.
gapnotify | The callback function.
cbprob | The current problem.
cbdata | The user-defined data passed as data when setting up the callback.
p_relgapnotifytarget | The value the MIPRELGAPNOTIFY control will be set to after this callback. May be modified within the callback in order to set a new notification target.
p_absgapnotifytarget | The value the MIPABSGAPNOTIFY control will be set to after this callback. May be modified within the callback in order to set a new notification target.
p_absgapnotifyobjtarget | The value the MIPABSGAPNOTIFYOBJ control will be set to after this callback. May be modified within the callback in order to set a new notification target.
p_absgapnotifyboundtarget | The value the MIPABSGAPNOTIFYBOUND control will be set to after this callback. May be modified within the callback in order to set a new notification target.
data | A user-defined data to be passed to the callback function, gapnotify.
priority | An integer that determines the order in which multiple estimate callbacks will be invoked. The callback added with a higher priority will be called before a callback with a lower priority. Set to 0 if not required.

Example
The following example prints a message when the gap reaches 10% and 1%

    void XPRS_CC gapnotify(XPRSprob prob, void* data,
      double* p_relgapnotifytarget, double* p_absgapnotifytarget,
      double* p_absgapnotifyobjtarget, double* p_absgapnotifyboundtarget)
    {
      double obj, bound, relgap;
      XPRSgetdblattrib(prob, XPRS_MIPOBJVAL, &obj);
      XPRSgetdblattrib(prob, XPRS_BESTBOUND, &bound);
      if (obj != 0.0 || bound != 0.0)
        relgap = fabs((obj - bound)/ max(fabs(obj), fabs(bound)));
      else
        relgap = 0.0;
      if (relgap<=0.10) {
        printf("Gap reached 10%");
        *p_relgapnotifytarget = 0.1;
      }
      if (relgap<=0.01) {
        printf("Gap reached 1%");
        *p_relgapnotifytarget = -1; /* Don't call gapnotify again */
      }
    }

    XPRSsetdblcontrol( prob, XPRS_MIPRELGAPNOTIFY, 0.10 );
    XPRSaddcbgapnotify( prob, gapnotify, NULL, 0 );
    XPRSmipoptimize(prob, "");

Further information
The target values that caused the callback to be triggered will automatically be reset to prevent the same callback from being fired again.
Related topics
MIPRELGAPNOTIFY, MIPABSGAPNOTIFY, MIPABSGAPNOTIFYOBJ, MIPABSGAPNOTIFYBOUND, XPRSremovecbgapnotify.
Parent Topic Console and Library Functions

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