Say you have some Mask Parameter named "Param", and you would like to pass the value contained by some variable named "Var" into Param. You can do:
set_param(gcb, 'Param', Var);
Note that gcb gets the name of the current block. If you are calling set_param in the callback function for Param, the current block will be the correct block. If you are calling set_param from somewhere other than the callback for Param, you may have to put the explicit blockname instead of gcb. To get this block name, just click on the block, and then run gcb in the matlab command line.
