# how to count the total number of recursion ?

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Kratos el 27 de Mzo. de 2015
Comentada: Andrew Newell el 27 de Mzo. de 2015
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.
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Andrew Newell el 27 de Mzo. de 2015
Editada: Andrew Newell el 27 de Mzo. de 2015
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
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Kratos el 27 de Mzo. de 2015
Editada: Kratos el 27 de Mzo. de 2015
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 el 27 de Mzo. de 2015
They must be defining it differently than I am. Just replace
num = 0;
by
num = -1;

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