# loop: stop if value repeats

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Niklas Kurz on 21 Jan 2021
Answered: Jan on 24 Jan 2021
In my case this is based on
N = Number
G = Guess
x = 1:N
R= mod(G^x,N)
if R repeats I want the calculation mod(G^x,N) to stop and tell me the steps P that it needed to to get to R again
for example if R = 1, 4 3, 2, 1 -stop, P = 4
##### 2 CommentsShowHide 1 older comment
Jan on 24 Jan 2021
The question is not clear yet. This makes it hard to find an answer.

Jan on 24 Jan 2021
N = Number;
G = Guess;
x = 1:N;
R = nan(1, N);
found = N;
for k = 1:N
R(k) = mod(G^x(k), N);
if any(R(1:k-1) == R(k))
found = k;
break
end
end
R = R(1:found)

Bob Thompson on 21 Jan 2021
I'm assuming you have all four of these commands within some kind of loop. Without the loop I have not tested what I'm going to suggest adding.
To do what you're asking you need to record all the values of R, this can be done by indexing R. If you aren't running an integer for loop, starting at 1, then you'll need to add a counter for each time you loop.
Then you just need an if check to determine if the loop needs to be broken.
N = Number
G = Guess
x = 1:N
R(count) = mod(G^x,N)
if sum(R==R(count))>1
P = length(R)-1;
break
end
end
Niklas Kurz on 23 Jan 2021
I want the loop to stop if it found a repeated number because I need it to count the period in order that I can continue processing wih it.

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