MATLAB: Problem while implementing “Gradient Descent Algorithm” in Matlab

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I'm solving a programming assignment in machine learning course. In which I've to implement "Gradient Descent Algorithm" like below
I'm using the following code
 data = load('ex1data1.txt');
 % text file conatins 2 values in each row separated by commas
 X = [ones(m, 1), data(:,1)];
 theta = zeros(2, 1);
 iterations = 1500;
 alpha = 0.01;
 function [theta, J_history] = gradientDescent(X, y, theta, alpha, num_iters)
 m = length(y); % number of training examples
 J_history = zeros(num_iters, 1);
 for iter = 1:num_iters
    k=1:m;
    j1=(1/m)*sum((theta(1)+theta(2).*X(k,2))-y(k))
    j2=((1/m)*sum((theta(1)+theta(2).*X(k,2))-y(k)))*(X(k,2))
    theta(1)=theta(1)-alpha*(j1);
    theta(2)=theta(2)-alpha*(j2);
    J_history(iter) = computeCost(X, y, theta);
 end
 end
 theta = gradientDescent(X, y, theta, alpha, iterations);
On running the above code I'm getting this error message

Best Answer

j2 is not a scalar, but you are trying to assign it to a scalar location theta(2).
Did you intend for this line
    k=1:m;
to be a for-loop
    for k=1:m
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