You forget the tanh function in the last computation in the part of def bottom_data_is():

[mikechen66]

Issue: lstm.py--the 98th line.

There is a problem with the code of line: self.state.h = self.state.s * self.state.o. You forget the tanh function. The formula is h_{t} = o_{t} * tanh(s_{t}). Therefore, the correct one is the line of code as follows.

self.state.h = tanh(self.state.s) * self.state.o

Pasted the partial lines of code as follows.

 def bottom_data_is(self, x, s_prev = None, h_prev = None):
    # if this is the first lstm node in the network
    if s_prev is None: s_prev = np.zeros_like(self.state.s)
    if h_prev is None: h_prev = np.zeros_like(self.state.h)
    # save data for use in backprop
    self.s_prev = s_prev
    self.h_prev = h_prev

    # concatenate x(t) and h(t-1)
    xc = np.hstack((x,  h_prev))
    self.state.g = np.tanh(np.dot(self.param.wg, xc) + self.param.bg)
    self.state.i = sigmoid(np.dot(self.param.wi, xc) + self.param.bi)
    self.state.f = sigmoid(np.dot(self.param.wf, xc) + self.param.bf)
    self.state.o = sigmoid(np.dot(self.param.wo, xc) + self.param.bo)
    self.state.s = self.state.g * self.state.i + s_prev * self.state.f
    self.state.h = self.state.s * self.state.o

[try1995]

self.state.h = self.state.o * np.tanh(self.state.s)

[cs-heibao]

@mikechen66
and also exists problem when do backpropagation, ignoring the derivation of tanh function

    def top_diff_is(self, top_diff_h, top_diff_s):
        # notice that top_diff_s is carried along the constant error carousel
        ds = self.state.o * top_diff_h + top_diff_s
        do = self.state.s * top_diff_h
        di = self.state.g * ds
        dg = self.state.i * ds
        df = self.s_prev * ds

ds = self.state.o *(1-self.state.s^2)* top_diff_h + top_diff_s;
do = np.tanh(self.state.s) * top_diff_h

[nicodjimenez]

I think you're right some / most implementations use the tanh but that's not how I defined the forward pass in the blog article:

https://nicodjimenez.github.io/2014/08/08/lstm.html

If you want to make a PR to add that as an option, that's fine with me.

[bot66]

yes