how to count the total number of recursion ?

Hello

I have a function

   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
   k = num + 1;
   num = [num k]
   end

For the number of counts, num I keep getting num = [0 1] How do I count the total number of recursion that occurs? I heard that we can make a helper function but I have no idea how to make one. Thank you.

Answer 1

[Andrew Newell]

The problem is that you're not passing num to collatz, so how can it know how many times it has been called? Here is a version that makes num an optional argument, so you don't need to provide it in your call:

function [out, num] = collatz(val,varargin)

if nargin >1
    num = varargin{1};
else
    num = 0;
end

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

Now if you try

[out,num] = collatz(4)

you get

out =

     1

num =

     3

[Kratos]

thanks for the help, but the .p soln file that was provided gives num of 2. Similarly when I do [out3 num3] = collatz(5) I get

out = 1 and num = 6

but the num is supposed to 5.

Thanks.

[Andrew Newell]

They must be defining it differently than I am. Just replace

num = 0;

by

num = -1;