How can i fix this error?

I am trying to solve the gradient of the logistic regression function using the following formula but getting the error "MATRIX DIMENSIONS MUST AGREE".

gradf =(-Y*exp(-Y.*X.'*w).*X)./1+exp(-Y.*X.'*w);

how to fix the error?

[Walter Roberson]

What is size(X) ? What is size(Y) ? What is size(w) ?

Why are you dividing by 1 ? Does your actual code have () around the 1+ ?

Why are you calculating exp(-Y.*X.'*w) twice instead of calculating it once and assigning to a variable and using the variable twice?

[Hp2609]

size(X)=5000*784

size(Y)=5000*1

size(w)=784*1

I am calculating twice because its the derivative for the sigmoid function.

Answer 1

[Walter Roberson]

size(X)=5000*784
size(Y)=5000*1
size(w)=784*1

OKay, so Y.*X.' would be (5000 x 1) .* (784 x 5000) which would be an error.

If you just happened to instead have

Y.*(X*w)

then that would be (5000 x 1) .* (5000 x 784 * 784 x 1) -> (5000 x 1) .* (5000 x 1) -> 5000 x 1

I am calculating twice because its the derivative for the sigmoid function.

So?

If you had

gradf =(-Y*exp(-Y.*X.'*w).*X)./1+exp(-Y.*X.'*w);

and supposing that was correct code, then

temp = exp(-Y.*X.'*w);
gradf = (-Y*temp.*X)./1 + temp

However since division by 1 is mostly useless, I suspect you are thinking of

temp = exp(-Y.*X.'*w);
gradf = (-Y*temp.*X)./(1 + temp)