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Re: Location of probability PDF's and CDF's in gnuplot?

 From: Paul Kienzle Subject: Re: Location of probability PDF's and CDF's in gnuplot? Date: Sat, 27 Aug 2005 00:44:51 -0400

Avocado:~ paulkienzle\$ locate prob.dem
/sw/share/doc/gnuplot/demo/prob.dem
/Users/paulkienzle/darwinports/dports/math/gnuplot/work/gnuplot-3.8h.0/ demo/prob.dem

The functions are defined in stat.inc in the same directory. For logistic it is:

# Logistic PDF
logistic(x)=lambda*exp(-lambda*(x-a))/(1.0+exp(-lambda*(x-a)))**2

Note that many statistical functions are defined in Octave, though in the case of logistic_pdf, it does not include the lambda and a parameters so you instead need to use:

y = lambda*logistic_pdf(lambda*(x-a))

to get the same function as gnuplot.

- Paul

On Aug 26, 2005, at 11:15 PM, Henry F. Mollet wrote:

Where are the probability PDF's and CDF's located in gnuplot so I can set the path that they can be found. When in my home directory and trying for example 'logistic(x)' the function cannot be found. After I load the demo 'prob.dem' and do a few functions and then quit, plot logistic(x) will work
using my own parameters for a and lambda.
Henry

"/usr/local/bin/gnuplot"
gnuplot> pwd
/Users/hfm
gnuplot> plot logistic(x)
undefined function: logistic

Statistical Library Demo, version 2.3
Copyright (c) 1991, 1992, Jos van de Woude, address@hidden
NOTE: contains 54 plots and consequently takes a lot of time to run
Press Ctrl-C to exit right now
gnuplot> plot logistic(x)  # Now I get a graph
gnuplot>

I assume that default value would be used for the parameters if I don't give
them but this is not the problem:
gnuplot> plot logistic (x)
undefined function: logistic
gnuplot> a = 0.0
gnuplot> lambda = 2.0
gnuplot> mu = a
gnuplot> sigma = pi/(sqrt(3.0) + lambda)
gnuplot> plot logistic (x)
undefined function: logistic

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Octave is freely available under the terms of the GNU GPL.

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