I am going to take my conclusion back. Just because Maxima gives an error message while plotting does not mean the function is only defined for positive x.
Learn, live.
R
------------Original Message------------
From: "Richard Hennessy"<rvh2007 at comcast.net>
To: fateman at cs.berkeley.edu
Date: Sat, Jun-7-2008 11:03 AM
Subject: RE: [Maxima] Bessel plotting problem
I think I made a mistake. What I wanted to plot was the real valued function (f+g+conjugate(f+g))/2 where f and g are linearly independent (complex) solutions to my differential eq. I tried using realpart() but that did not work. I should have tried the following.
plot2d(-(sqrt(3)/2-%i/2)*%i*'(bessel_y(1/6,-x^3/3))+'(bessel_j(1/6,-x^3/3))*sqrt(x),[x,-20,.001], plot_format,gnuplot]), orthopoly_returns_intervals : false;
That worked.
The domain of the bessel_j or bessel_y function must be positive x only since when I try
plot2d(-(sqrt(3)/2-%i/2)*%i*'(bessel_y(1/6,-x^3/3))+'(bessel_j(1/6,-x^3/3))*sqrt(x),[x,-15,15],[plot_format,gnuplot]), orthopoly_returns_intervals : false;
I get
-->
***MESSAGE FROM ROUTINE DBESY IN LIBRARY SLATEC. ***POTENTIALLY RECOVERABLE ERROR, PROG ABORTED, TRACEBACK REQUESTED * X LESS THAN OR EQUAL TO ZERO * ERROR NUMBER = 2 * ***END OF MESSAGE ***JOB ABORT DUE TO UNRECOVERED ERROR.0 ERROR MESSAGE SUMMARY LIBRARY SUBROUTINE MESSAGE START NERR LEVEL COUNT SLATEC DBESY X LESS THAN OR EQUAL 2 1 1
When x is positive, the plot shows only the second and third quadrants with actual points. I think the first a fourth are not in the domain since I get this ugly error message when it is done.
I would call this a bug, I am not sure if it is. Is there a reason for the restriction x > 0?
Rich
------------Original Message------------
From: "Richard Fateman" <fateman at cs.berkeley.edu>
To: "'Richard Hennessy'" <rvh2007 at comcast.net>
Date: Sat, Jun-7-2008 10:11 AM
Subject: RE: [Maxima] Bessel plotting problem
I haven't tried it, but how about removing the ' and
doing plot2d( realpart( ....)..)
or plot2d ('(realpart( ...) ..))..
RJF