ode45 produces incorrect results

Tue Apr 7 17:37:24 CDT 2009

To: bug at octave.org
Subject: ode45 produces incorrect results
--------
Bug report for Octave 3.0.1 configured for x86_64-pc-linux-gnu

Description:
-----------

f=@(t,u) ([u(2); -sin(u(1))+cos(t)/3]);
t_range = [0; 40]; u_0 = [0; 0];
[t_steps, u] = ode45(f, t_range, u_0);
plot(t_steps, u);

This should give the trajectory of a pendulum. Up to a point the graph
looks good, but then it suddenly diverges. It should look like the
graph here:
http://mo.mathematik.uni-stuttgart.de/kurse/kurs4/seite50.html

Configuration (please do not edit this section):
-----------------------------------------------

uname output:     Linux kubuntu 2.6.27-11-generic #1 SMP Thu Jan 29
19:28:32 UTC 2009 x86_64 GNU/Linux configure opts:
'--host=x86_64-linux-gnu' '--build=x86_64-linux-gnu' '--prefix=/usr'
'--datadir=/usr/share' '--libdir=/usr/lib' '--libexecdir=/usr/lib'
'--infodir=/usr/share/info' '--mandir=/usr/share/man'
'--with-blas=-lblas-3gf' '--with-lapack=-llapackgf-3' '--with-hdf5'
'--with-fftw' '--enable-shared' '--enable-rpath' '--disable-static'
'build_alias=x86_64-linux-gnu' 'host_alias=x86_64-linux-gnu' 'CC=gcc'
'CFLAGS=-g -O2' 'LDFLAGS=-Wl,-Bsymbolic-functions' 'CPPFLAGS='
'CXX=g++' 'CXXFLAGS=-g -O2' 'F77=gfortran' 'FFLAGS=-g -O2' Fortran
compiler: gfortran FFLAGS:           -O2 -g F2C:              @F2C@
F2CFLAGS:         @F2CFLAGS@ FLIBS:
-L/usr/lib/gcc/x86_64-linux-gnu/4.3.1
-L/usr/lib/gcc/x86_64-linux-gnu/4.3.1/../../../../lib -L/lib/../lib
-L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/4.3.1/../../.. -lhdf5
-lz -lgfortranbegin -lgfortran -lm CPPFLAGS: INCFLAGS:         -I. -I.
-I./liboctave -I./src -I./libcruft/misc C compiler:       gcc, version
4.3.1 (Ubuntu 4.3.1-8ubuntu3) CFLAGS:           -O2 -g
CPICFLAG:         -fPIC C++ compiler:     g++, version 4.3.1
CXXFLAGS:         -O2 -g CXXPICFLAG:       -fPIC LD_CXX:           g++
LDFLAGS: LIBFLAGS:         -L. RLD_FLAG:         -Wl,-rpath
-Wl,/usr/lib/octave-3.0.1 BLAS_LIBS:        -llapackgf-3 -lblas-3gf
FFTW_LIBS:        -lfftw3 LIBS:             -lreadline  -lncurses -ldl
-lhdf5 -lz -lm LEXLIB: LIBGLOB:          
SED:              /bin/sed
DEFS:

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User-preferences (please do not edit this section):
--------------------------------------------------

  EDITOR = emacs
  EXEC_PATH
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