How can i fix this error?

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Hp2609
Hp2609 2021-5-4
回答： Walter Roberson 2021-5-4
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?
  2 个评论
Walter Roberson
Walter Roberson 2021-5-4
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
Hp2609 2021-5-4
size(X)=5000*784
size(Y)=5000*1
size(w)=784*1
I am calculating twice because its the derivative for the sigmoid function.

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Walter Roberson
Walter Roberson 2021-5-4
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)

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