Hi Steffen,
If you have version 7 or 7.5, one possible workaround is to define/code your function as an Origin C function, and then just call the OC function from the Function Plot.
For example, you can define a function in OC such as:
double myfunc(double x)
{
return sin(x)/x;
}
and then call that from the Function Plot as:
F1(x)=myfunc(x)
With Origin C, you will have no limitations on number of characters etc.
Easwar
OriginLab