How to keep track of recursive call on my function collatz?

Question

I am trying to keep track of how many times the function call itself. I have tried setting up num as 0 and putting num = num+1 at the end but I keep getting 1. How do I fix this?

function [out num] = collatz(val)
num = 0;
if val == 1
   out = 1;
elseif mod(val, 2) == 0
   out = collatz(val/2);
else 
   out = collatz(3*val+1);
end
num = num+1;
end

Thank you.

Answer 1

A possible approach is to use a global variable to count the number of calls. You need to declare that variable as global

• in the workspace from which you call collatz the first time; and
• within the function.

The function is thus defined as:

function out = collatz(val)
global num %// declare as global within the function
num = num+1; %// increase call counter
if val == 1
   out = 1;
elseif mod(val, 2) == 0
   out = collatz(val/2);
else 
   out = collatz(3*val+1);
end
end

And then, from the command line:

>> clear all
>> global num %// declare as global in workspace
>> num = 0; %// initiallize to 0
>> collatz(5)
ans =
     1
>> num %// see value of num
num =
     6