Hello!
Seeing the syntax with which you have called the ode45 function, I think the issue is with the parameters passed. The function "volterrab" has been passed in inverted commas. But the function syntax needs a function handle as the first input argument. So, try the syntax:
[t,x]=ode45(@volterra, ts,x0);
For more information, you may refer to the following documentation:
Function Handles: https://www.mathworks.com/help/matlab/matlab_prog/pass-a-function-to-another-function.html
Hope this helps!
