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checking if variable is defined



Helle there,

I would like to plot a variable, but only if it is existing. When the
Variable is undefined, nothing should happen. So I am searching for an
expression for the if  statement. Does anybody know an expression like:
if ( vaiable_name existing) then...

Thanks

Dominik


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_____________________________
Dominik Paul
dpaul@ukl.uni-freiburg.de
Universitätsklinikum Freiburg
Abt. PET/Nuklearmedizin