Initializing help system before first use

problem.addcbgapnotify

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.
Synopsis

problem.addcbgapnotify(callback, data, priority)

(RelGapNotify, AbsGapNotify, AbsGapNotifyObj, AbsGapNotifyBound) = callback(my_prob, my_object)
Arguments
callback 
The callback function.
data 
A user-defined object that will be passed into the callback callback.
priority 
An integer that determines the order in which multiple gap notification callbacks will be invoked. The callback added with the higher priority will be called before a callback with a lower priority. Set to 0 if not required.
my_prob 
The current problem.
my_object 
The user-defined object passed as data when setting up the callback with addcbgapnotify.
RelGapNotify 
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. Can be None.
AbsGapNotify 
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. Can be None.
AbsGapNotifyObj 
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. Can be None.
AbsGapNotifyBound 
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. Can be None.
Example
The following example prints a message when the gap reaches 10% and 1% 
def gapnotify(prob, object):

    obj = prob.attributes.mipobjval
    bound = prob.attributes.bestbound

    # If no solutions were found, just return a tuple of None's
    if prob.attributes.mipsols == 0:
        return None, None, None, None

    if obj != 0 and bound != 0:
        relgap = abs((obj - bound) / max(abs(obj), abs(bound)))
    else:
        relgap = 0

    newRelGapNotifyTarget = -1

    if relgap <= 0.1:
        print('Gap reached 10%')
        newRelGapNotifyTarget = 0.1

    if relgap <= 0.01:
        print('Gap reached 1%')
        newRelGapNotifyTarget = -1 # Don't call gapnotify again

    # return a quadruple with new values, or
    # None for those that should not be set
    return (newRelGapNotifyTarget, None, None, None)

prob.controls.miprelgapnotify = 0.1
prob.addcbgapnotify(gapnotify, None, 0)
prob.mipoptimize('')
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, problem.removecbgapnotify.

Parent Topic Xpress problem methods

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