Reassigning array values in for loop

I want to make a random number generator. It uses 3 formulas so I have 3 arrays which will store the values that are generated.

I currently have a for loop that generates the numbers but for some reason it is not updating the arrays. I tested the formulas by writing specific values for n and it does work so the problem seems to be in the loop.

Can anyone see why it is not working?

            a1 = 0; a2 = 63308; a3 = -183326;
            b1 = 86098; b2 = 0; b3 = -539608;
            m1 = 2147483647; m2 = 2145483479;

            %create an array with 10000 spaces
            Z = zeros(1,10000);
            X = zeros(1,10000);
            Y = zeros(1,10000);

            %To compute the random numbers, I need a seed for x and y
            X(1) = 1; X(2) = 4; X(3) = 11;
            Y(1) = 2; Y(2) = 9; Y(3) = 17;
          

            x_n = @(n) mod((a1*X(n-1) + a2*X(n-2) + a3*X(n-3)),m1);
            y_n = @(n) mod((b1*Y(n-1) + b2*Y(n-2) + b3*Y(n-3)),m2);
            z_n = @(n) mod((x_n(n) - y_n(n)),m1);
            
            for i=4:10000
                X(i) = x_n(i);
                Y(i) = y_n(i);
                Z(i) = z_n(i);
            end
            disp(Z)

[dpb]

>> [X(1:10);Y(1:10);Z(1:10)]
ans =
1            4           11        69906   2.1474e+09   2.1455e+09            0            0            0            0
2            9           17   3.8445e+05   2.1406e+09   2.1363e+09            0            0            0            0
0            0            0   2.1472e+09   6.8197e+06   9.1569e+06            0            0            0            0
>> 

Seems to do something for the variables you've calculated -- your loop only iterates over 4:6 so nothing other than those values can change.

[Michelle Lear]

Oh, I had changed it to see if it would change a few but even when it's i=4:10000, it doesnt update for me. But I see it updates on yours, so maybe it's an error on my laptop

Answer 1

[David Hill]

You are overflowing floating point numbers.

import java.math.*
a1 = BigInteger('0'); a2 = BigInteger('63308'); a3 = BigInteger('-183326');
b1 = BigInteger('86098'); b2 = BigInteger('0'); b3 = BigInteger('-539608');
m1 = BigInteger('2147483647'); m2 = BigInteger('2145483479');
%To compute the random numbers, I need a seed for x and y
X(1:3)=[BigInteger('1'),BigInteger('4'),BigInteger('11')];
Y(1:3) =[BigInteger('2'),BigInteger('9'),BigInteger('17')];
x_n = @(n) a1.multiply(X(n-1)).add(a2.multiply(X(n-2))).add(a3.multiply(X(n-3))).mod(m1);
y_n = @(n) b1.multiply(Y(n-1)).add(b2.multiply(Y(n-2))).add(b3.multiply(Y(n-3))).mod(m2);
z_n = @(n) x_n(n).subtract(y_n(n)).mod(m1);
for i=4:10000
    X(i) = x_n(i);
    Y(i) = y_n(i);
    Z(i) = z_n(i);
end