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[Octave-bug-tracker] [bug #56118] (optim) logistic_regression gives inco
From: |
Muhali |
Subject: |
[Octave-bug-tracker] [bug #56118] (optim) logistic_regression gives incorrect result |
Date: |
Thu, 11 Apr 2019 11:08:23 -0400 (EDT) |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0 |
URL:
<https://savannah.gnu.org/bugs/?56118>
Summary: (optim) logistic_regression gives incorrect result
Project: GNU Octave
Submitted by: muhali
Submitted on: Thu 11 Apr 2019 08:08:21 AM PDT
Category: Octave Forge Package
Severity: 3 - Normal
Priority: 5 - Normal
Item Group: None
Status: None
Assigned to: None
Originator Name:
Originator Email:
Open/Closed: Open
Discussion Lock: Any
Release: 5.1.0
Operating System: GNU/Linux
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Details:
Applying a logistic regression in the following way
pkg load optim
x = (1:20)' ; y = [zeros(10, 1) ; ones(10,1)] ;
Pfun = @(p) exp(p(1) - p(2) * x) ./ (1 + exp(p(1) - p(2) * x)) ; Pin = [0 0]'
;
p1 = nonlin_curvefit (Pfun, Pin, x, y) ;
[p2(1) p2(2)] = logistic_regression(y, x) ;
subplot(2,1,1) ;
plot(x, y, "x", x, Pfun(p1), "-") ;
set(gca, "box", "off")
subplot(2,1,2) ;
plot(x, y, "x", x, Pfun(p2), "-") ;
set(gca, "box", "off")
one sees that the result cannot be correct. The reason is a mismatch between
the function description in the help text and what is actually programmed.
Using Pfun(-p2) gives the correct result.
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<https://savannah.gnu.org/bugs/?56118>
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