I want to double all the points on the elliptic curves in matlab

I want to double all the points on the elliptic curves .I have written a code but it gives error. Matrix A contains few points but this code dosnot work.

%curve equation is y^2=x^3+17 mod 313
A=[[199 29] [200 26] [202 14] [203 110] [209 102]];
for i=1:5
B=multell(A(i),2,0,17,313);
end
B

[Bruno Luong]

You have issue with construction and indexing of your A matrix.

Please revise MATLAB syntax and array indexing.

Answer 1

[Bruno Luong]

See this post there a an algo to demonstrate doubling and adding points in EC.

Adapt for your case

% EL parameters
a = 0;
b = 17;
% Group Z/pZ parameter
p = 313;
A=[[199 29]; [200 26]; [202 14]; [203 110]; [209 102]]

B = zeros(size(A));
% Point
for k=1:size(A,1)
    G = A(k,:);
    % Compute G2 = 2*G
    x = G(1);
    y = G(2);
    d = mod(2*y,p);
    [~,invd,~] = gcd(d,p);
    n = mod(3*x*x + a,p);
    lambda = mod(n*invd,p);
    x2 = mod(lambda*lambda - 2*x,p);
    y2 = mod(lambda*(x-x2)-y,p);
    G2 = [x2 y2];
    B(k,:) = G2;
end
B

[sadiqa ilyas]

i want to double all the points in matrix A at a time.

[sadiqa ilyas]

It works. Thanks a lot