Dear @raksha
With fluka4 when the parenthesis expansion generates a divergent number of terms, and fluka might fails to expand it. In this case, you can force it to run with the “online evaluation” by setting the variable “Paren:” to some small integer number bigger than zero, eg. 1 (force the online for everything, 10-20 allow expansion up to 10 or 20 times longer length of expression)
then the simulation will be carried out correctly.
The Parenthesis term is a multiplicative factor of the number of terms
Please note that using the “online parenthesis expansion” it will run slower in the respective region.