theano的T.grad如何计算

f(x) = x*x + x - 2Graph =          ADD         /   \        MUL  SUB       /  \  /  \       x  x  x  2Chain rule for ADD=> (a(x)+b(x))' = a'(x) + b'(x)Chain rule for MUL=> (a(x)*b(x))' = a'(x)*b(x) + a(x)*b'(x)Chain rule for SUB=> (a(x)-b(x))' = a'(x) - b'(x)The derivative of x is 1, and the derivative of a constant is 0.Derivative graph (not optimized yet) =          ADD         /   \       ADD    SUB      /  |    |  \   MUL  MUL   1   0  /  |  |  \ 1   x  x   1Derivative graph (after optimization) =          ADD         /   \       MUL    1      /   \     2     xSo: f'(x) = 2*x + 1