How can I fix the error in the given below program?

clc;
clear all;
close all;

disp('***** y^2 = x^3 + ax + b mod p *****');
n=input('insert prime p: ');
a=input('insert coefficient a: ');
b=input('insert coefficient b: ');
x=[0:n-1];
y=[0:n-1];
figure
for i=1:n
    for j=1:n
        if rem((vpi(y(j))^2)-(vpi(x(i))^3)-a*(vpi(x(i)))-b,n)==0
            plot(x(i),y(j),'r o');
            hold on;
        end
    end
end
grid;
hold off;

Maximum variable size allowed by the program is exceeded.

Error in sir (line 9)
x=[0:n-1];

[Stephen23]

What value of n did you use?

[Manoj]

n=730750818665451459101842416358141509827966272589 a=361221832160941494419407229753461201862246374272 b=346937986907100912443917613080678747571038706015

[Star Strider]

Using double-precision representation, ‘x’ would then require 5.8460e+048 bytes.

Answer 1

[Jan]

input replies a double. According to the IEEE754 standard, a double has about 15 significant digits. Therefore you cannot input "730750818665451459101842416358141509827966272589" and expect it to be stored exactly. Even using the command vpi afterwards does not reconstruct the rounded digits magically. You can insert directly:

n = 7.30750818665451e47

etc. But then the shown algorithm cannot produce a meaningful output.

In addition creating a vector 0:7.3e47 needs 7.3e47*8 Bytes. There is no computer on the earth with 5.8*10^41 GigaByte RAM. And you want to create 2 of these vectors and process them in two nested loops over all elements?!

The universe is too small for this computation. Then most likely Matlab is, too. The message

 Maximum variable size allowed by the program is exceeded.

is pure understatement.