Matlab logistic回归成本的向量化
我在matlab中有逻辑回归中的成本代码:Matlab logistic回归成本的向量化,matlab,vectorization,logistic-regression,Matlab,Vectorization,Logistic Regression,我在matlab中有逻辑回归中的成本代码: function [J, grad] = costFunction(theta, X, y) m = length(y); % number of training examples thetas = size(theta,1); features = size(X,2); steps = 100; alpha = 0.1; J = 0; grad = zeros(size(theta)); sums = []; result = 0; fo
function [J, grad] = costFunction(theta, X, y)
m = length(y); % number of training examples
thetas = size(theta,1);
features = size(X,2);
steps = 100;
alpha = 0.1;
J = 0;
grad = zeros(size(theta));
sums = [];
result = 0;
for i=1:m
% sums = [sums; (y(i))*log10(sigmoid(X(i,:)*theta))+(1-y(i))*log10(1-sigmoid(X(i,:)*theta))]
sums = [sums; -y(i)*log(sigmoid(theta'*X(i,:)'))-(1-y(i))*log(1-sigmoid(theta'*X(i,:)'))];
%use log simple not log10, mistake
end
result = sum(sums);
J = (1/m)* result;
%gradient one step
tempo = [];
thetas_update = 0;
temp_thetas = [];
grad = temp_thetas;
for i = 1:size(theta)
for j = 1:m
tempo(j) = (sigmoid(theta'*X(j,:)')-y(j))*X(j,i);
end
temp_thetas(i) = sum(tempo);
tempo = [];
end
grad = (1/m).*temp_thetas;
% =============================================================
end
我需要矢量化它,但我不知道它是如何做到的,为什么?我是一名程序员,所以我喜欢for的。但要将其矢量化,我是空白的。有什么帮助吗?谢谢。代码应该是什么
function [J, grad] = costFunction(theta, X, y)
hx = sigmoid(X * theta);
m = length(X);
J = (-y' * log(hx) - (1 - y')*log(1 - hx)) / m;
grad = X' * (hx - y) / m;
end
function[J,grad]=costFunction(θ,X,y)
hx=乙状结肠(X'*θ);
m=长度(X);
J=总和(-y*log(hx)-(1-y)*log(1-hx))/m;
梯度=X'*(hx-y)/m;
结束
这太简单了,想解释一下吗?:)通过使用矩阵乘法,可以去掉i=1:m的和i=1:size(θ)的。然后代码变小:)J=-(1/m)*(log(hX')*y+log(1-hX')*(1-y))代码>@FranckDernoncourt我想出了同样的解决方案。这是令人沮丧的,因为他们经常引用theta'*X
,但它与他们的向量构造不兼容。@FranckDernoncourt为什么必须求和?J不是1x1向量吗?或者只是将其作为标量而不是向量返回?