index must b positive?plz help

clc;clear all;
g_db=[0:1:10];

g=10.^(g_db/10);
alpha=2;
c=1;
M=2;
syms y
   r=0;
for j=2:M

p=((-1)^j)*(factorial(M)/factorial(j)*factorial(M-j))*exp(-(g.*y(1-(1/j))));
r=r+p;
t=r*(1/M)
end
x=((y.^(alpha-1)).*exp(-y./c))/((gamma(alpha))*(c^alpha));
z=t*x;
semilogy(g_db,z);
hold on

Answer 1

[Walter Roberson]

You have the expression

p=((-1)^j)*(factorial(M)/factorial(j)*factorial(M-j))*exp(-(g.*y(1-(1/j))));

The y(1-(1/j)) part of that says to index the variable y at index (1-(1/j)) . As all of your j are at least 2, 1/j is less than 1 so 1-1/j is not a positive integer.

Perhaps you wanted to code multiplication instead of indexing. y*(1-(1/j))