@John Fredsted thank you for your help

@John Fredsted  actually i want to use  a loop for piece-wise function then to find the value of Z(n,m) by using the values of R(n,m) and Theta for different values of m, like m =-4,-3,-2,-1,01,2,3,4 and n=0,1,2,3,4. ,  

@Preben Alsholm thanks for your kind reply. I tried the command but actually i want to get the value of Z(n,m) as i mentioned below. But i am not getting any result after execution.