Equation and neural networks

i am using neural network to predict the output from 2 inputs, can matlab develop an equation based on the calculation for the predicted output?

Let say, here are my input and output

• input >> output
• 1 1 >> 2
• 2 2 >> 4

and next sequence will be predicted by neural network which is

• 3 3 >> ?

Is there any function that i can use to know the equation used by matlab to calculate next sequence (eg. output= input1 +input2)?

Answer 1

[Greg Heath]

HiddenVariableMatrix = tanh( InputWeightMatrix*InputVariableMatrix + Biasvector1);

OutputVariableMatrix = Biasvector2 + LayerWeightMatrix*HiddenVariableMatrix;

[azie]

thanks for your response. your answer is actually a coding for ff neural network right? what i want is, the coding/function for developing the specific equation for output. which from your answer is

OutputVariableMatrix = Biasvector2 + LayerWeightMatrix*tanh( InputWeightMatrix*InputVariableMatrix + Biasvector1);

From my understanding, i need to code the above line in my programming. but is there any function that can create specifically an output equation together with assigning weight?

[Greg Heath]

All calculations are obtained via MATLAB functions which perform all of the calculations within.

See the documentation and demos in the Neural Network Toolbox.

Answer 2

[KK]

Hi Greg

I am new to Neural Network and try to learn the theory/formula part such as formulas. Where can I find the equation you pointed out OutputVariableMatrix = Biasvector2 + LayerWeightMatrix*tanh( InputWeightMatrix*InputVariableMatrix + Biasvector1);

under Matlab Neural Netowrk Toolbox?

I try to know other formulas for non-default settings. Could you also recommend some fundamental articles for learning neural network. It is so easy to find the formula about SVM. But I googled a while and could not find a simple clear article about the output equations under neural network. Thanks!

KK

[Greg Heath]

I don't know where MATLAB has explicitly posted that equation. Replace tanh with tansig and try searching in the NEWSGROUP and ANSWERS.

Try

 IW LW TANSIG

Hope this helps.

Greg

Answer 3

[Abdelmalek Bellal]

Hello Greg,

I used a code for the exraction of wieghts and Baises but the collected vector of predictions by runing the ANN model is diffrent from what I am getting by using the mathematical equation. I believe the extracted weights are not the same weights that are use by the model or the equation is incorrcet? I tried multiple times but I am getting abnormal values that are negative and widely far from what I am getting from collceted vector of prediction with runing the model.

I added exponential to the output y because I am using Log transform.

Below is the obtained predictions from runing the model and the actual outputs: (reasonable)