Problems with NS2 simulator

I am using Cygwin on my windows 8.1 and trying to run a tcl file but I encountered error “nam: no display name and no $DISPLAY environment variable” every time when I try to run.

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I even tried to export the $DISPLAY as
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I’m don’t entirely understand how this question is related to BeagleBoard, since you’re attempting to run an X application on Cygwin. Have you actually installed the XOrg packages which enable Cygwin to do so, and lauched the xorg service?

so, when you export $DISPLAY it’s not complaining about display any more, right?
what exactly happens, though? do you see any graphical output? what gets printed on the stdout of the console from which you run your program?
What is it supposed to do?

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