Wondering what is "Goal Function value" in CST

Hi all,
I'm using the GA optimizer of CST microwave studio, anybody can tell me what is the "goal function value" stated in the optimization info page?
It seem to drop and slowly approach 0 when the optimization run, so what is this "goal function value" indicate?
Thanks in advance.

Each optimization has a goal. Otherwise the program does not know in which direction some parameters have to be modified. Such a goal can be power minimization or bandwidth tuning or something else.
Was that your question?

Thanks for reply.
The goal function value that i mention is like the picture below, this value is show when the optimization is running, observe that it is not the goal (target).

Hi winsonwhy,
As far as I can see, there was an optimizer run with some results (goal function value). To start this run the goal function was specified before of course.
Thus, what is the goal you have in mind?

Hi,
I'm trying to optimize the gain of my antenna to exceed the preset goal value say larger than 15dBi.
Observed that each time when the optimizer successful optimized the antenna structure to have gain larger than 15dBi (optimization stop automatic) the goal function value will drop to zero.
Is there any relation between "goal function value" and "goal"?