getting error "Undefined function or method 'logistic' for input arguments of type 'double'.""

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I have written a code based on neural network and when I ma trying to run code getting error as "Undefined function or method 'logistic' for input arguments of type 'double'" I have given the portion of code where getting error.
double logistic(x)
if(x > 100.0)
x = 1.0;
else if (x < -100.0)
x = 0.0;
else x = 1.0/(1.0+exp(-x));
x;
end
end
function [V_OUT]= feed_forward_signals(MAT_INOUT, V_IN, V_OUT, V_BIAS, size1, size2, layer)
for row = 1:size2
V_OUT(row)=0;
for col = 1:size1
V_OUT(row)=V_OUT(row)+MAT_INOUT(row,col)*V_IN(col);
end
V_OUT(row)=V_OUT(row)+V_BIAS(row);
end
if(layer==0)
V_OUT(row) = tanh(V_OUT(row));
end
if(layer==1)
V_OUT(row) = logistic(V_OUT(row));
please help
end

Accepted Answer

Greg Heath
Greg Heath on 29 Jun 2015
If you have the Neural Network Toolbox just use
LOGSIG or TANSIG
otherwise, just use TANH.
Also see
Subject: NEURAL NET TRAINING SPEED USING A MODIFIED ELLIOT SIGMOID
From: Greg Heath
Date: 14 Oct, 2012 06:18:08
Hope this helps.
Thank you for formally accepting my answer
Greg
  2 Comments
vandana
vandana on 30 Jun 2015
Hi, thanks for your reply. but does LOGSIG or TANSIG functions will give the same results as logistic. because I am getting good results with logistic function only. TANH is not giving good results.
Greg Heath
Greg Heath on 30 Jun 2015
[x,t] = simplefit_dataset;
z = [ x; t];
1. TANSIG is MATLAB's version of TANH.
y1 = tansig(z);
y2 = tanh(z);
>> ans = minmax(y1-y2)
ans = -3.3307e-16 3.3307e-16
-3.3307e-16 3.3307e-16
2. LOGSIG is MATLAB's version of the LOGISTIC.
3. It has been demonstrated in the comp.ai.neural-nets FAQ that tansig hidden nodes are better than logsig when inputs have zero mean.
Neural Network FAQ, part 1 of 7: Introduction - SAS
ftp://ftp.sas.com/pub/neural/FAQ.html
Hope this helps.
Greg

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