Explicit equation did not give the result same as the output value obtained from ANN model

I developed my ANN model using tangsig activation function for the hidden layer and purelin for the output layer. I have saved the model beforehand so that weight and bias will not change after I run the model again. I obtain the weight and bias from the network by using following commands:

InputWeight = LTnet2.IW{1,1}
LayerWeight = LTnet2.LW{2,1}
InputBias = LTnet2.b{1,1}
LayerBias = LTnet2.b{2,1}

I used the weights and bias to form the explicit equations where:

Layer 1 : y1 = tanh(X*InputWeight+InputBias)

Layer 2 : y2 = y1*LayerWeight+LayerBias

However, after I developed the explicit equations and want to test the new data with the equations to predict the output, the value is different from what is predicted from the model. Can anyone advise me what is the problem?

[Shing Mei Chiew]

can anyone answer me?