Matrix multiplication in a for-loop

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I'm currently trying to transform this expression:
k = 1:m;
t1 = sum((theta(1) + theta(2) .* X(k,2)) - y(k));
t2 = sum(((theta(1) + theta(2) .* X(k,2)) - y(k)) .* X(k,2));
theta(1) = theta(1) - (alpha/m) * (t1);
theta(2) = theta(2) - (alpha/m) * (t2);
into a for loop expression, so that it will work for longer theta vectors. So far I came up with this:
for j=1,length(theta)
t = sum(((X * theta)- y) .* X(:,j));
theta(j) = theta(j) - (alpha/m) * t;
end
But the values for theta(2) are not updated. What am I doing wrong?

Accepted Answer

JESUS DAVID ARIZA ROYETH
JESUS DAVID ARIZA ROYETH on 5 Feb 2020
you have 1,length(theta), change it by 1:length(theta) :
for j=1:length(theta)
t = sum(((X * theta)- y) .* X(:,j));
theta(j) = theta(j) - (alpha/m) * t;
end

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