Neural Network layer design

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MatLab

network

Am kinda new to neural network. This is one piece of code I've tried in Matlab

P= 0 + (rand(1) * 10);

T = (P-1)/(P+1);

net = newelm(P,T,5);

net = train(net,P,T);

Y = sim(net,P);

Now when i type net.B{1} and net.LW{1} in the command window of matlab, i get the bias weights and layer weights, but i also find that these weight values keep changing according to input values.

So can i have a predefined weight value, the one that doesn't change, for a particular function(and for any value of input), such that using these weight values i can design a neural network for a particular function. Like here I have T which is related to P by a particular equation.

Any help will be appreciated.
Thanks:)