梯度下降

h(x)=ni=0θixi
J(θ)=12mi=1(hθ(x(i))y(i))2
θi:=θiαθiJ(θ)

θiJ(θ)=θi12(hθ(x)y)2=212(hθ(x)y)θi(hθ(x)y)=(hθ(x)y)xi

θi:=θiα(hθ(x)y)xi
θi:=θiαmj=1(hθ(x(j))y(j))x(j)i
θ=(xTx)1xTy

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