scale data for NN
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Hi,
How do I scale data in a neural network multilayer backpropagation?
采纳的回答
Greg Heath
2012-5-17
You do not have to scale the data because variables are AUTOMATICALLY scaled to {-1,1} with MAPMINMAX by NEWFF, FITNET, PATTERNNET AND FEEDFORWARDNET.
The command
type feedforwardnet
yields these commands
========================
% Inputs
net.numInputs = 1;
net.inputConnect(1,1) = true;
net.inputs{1}.processFcns = {'removeconstantrows','mapminmax'};
% Outputs
net.outputConnect(Nl) = true;
net.outputs{Nl}.processFcns = {'removeconstantrows','mapminmax'};
===================================================
If you wish, you can replace either occurrance of MAPMINMAX with 'mapstd' (zero-mean/unit-variance) or 'none'.
I prefer to use MAPSTD before creating the net to try to understand the input/output relationships via plots, correlation coefficients and outliers.
Then I accept the automatic minmax normalization instead of removing or changing it.
Hope this helps.
Greg
更多回答（1 个）
Greg Heath
2012-5-18
1. Derive a linear tranformation xn(x) = a.*x + b such that
xn( x = min(x) ) = -1
xn( x = max(x) ) = +1
2. Derive a linear tranformation xn(x) = a.*x + b such that
mean(xn) = 0
var( xn ) = 1
Hope this helps.
Greg
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