[Maxima-bugs] [ maxima-Bugs-1981628 ] a bug of radcan() and radexpand

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Bugs item #1981628, was opened at 2008-06-02 05:45
Message generated for change (Comment added) made by crategus
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Category: Lisp Core - Simplification
Group: None
>Status: Closed
>Resolution: Duplicate
Priority: 5
Private: No
Submitted By: Satoshi Adachi (satoshi_adachi)
Assigned to: Nobody/Anonymous (nobody)
Summary: a bug of radcan() and radexpand

Initial Comment:
Dear Developers of Maxima,

radcan() does not behave in the correct way.

In the online desription of radcan() with the correction of a misprint,
which is informed in a separate report by me, it is written that

 -- Function: radcan (<expr>)
     ...
     ...
     When `radexpand' is `false', certain transformations are inhibited.
     `radcan (sqrt (1-x))' remains `sqrt (1-x)' and is not simplified
     to `%i sqrt (x-1)'.  `radcan (sqrt (x^2 - 2*x + 1))' remains
     `sqrt (x^2 - 2*x + 1)' and is not simplified to `x - 1'.
     ...
     ...

The control by the variable `radexpand' does not work in the present Maxima.
A demonstration program is as follows:
-------------------------------------------------------------------------------
/*
 *   a_bug_of_radcan.maxima:
 *
 *   S.Adachi 2008/06/01
 */

display2d:false;

radexpand; /* Inspect the value of `radexpand' */

radcan(sqrt(x^2-2*x+1)); /* expected to reduce to x-1 */

radexpand:false;

radcan(sqrt(x^2-2*x+1));  /* expected to remain sqrt(x^2-2*x+1) */

/* END */
-------------------------------------------------------------------------------

The result of execution is as follows:
-------------------------------------------------------------------------------
Maxima 5.14.0cvs http://maxima.sourceforge.net
Using Lisp GNU Common Lisp (GCL) GCL 2.6.7 (aka GCL)
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1)                    batch(a_bug_of_radcan.maxima)

batching #p/Volumes/HFS+2/home/adachi/work/301/a_bug_of_radcan.maxima
(%i2)                          display2d : false
(%o2) false
(%i3) radexpand
(%o3) true
(%i4) radcan(sqrt(1-2*x+x^2))
(%o4) x-1
(%i5) radexpand:false
(%o5) false
(%i6) radcan(sqrt(1-2*x+x^2))
(%o6) x-1
(%o7) "a_bug_of_radcan.maxima"
-------------------------------------------------------------------------------

If `radexpand' is `false', `radcan(sqrt(x^2-2*x+1))' is expected to remain
`sqrt(x^2-2*x+1)'. However, Maxima returns `x-1' in reality.
This is a bug.

I think that this is a very serious bug of radcan().
Please fix it.

Sincerely yours,
Satoshi Adachi



----------------------------------------------------------------------

>Comment By: Dieter Kaiser (crategus)
Date: 2009-11-28 22:25

Message:
This bug report is a duplicate of the bug report ID: 1977146 - radexpand
does not work as explained in documentation.

Closing this bug report as a duplicate:

Dieter Kaiser

----------------------------------------------------------------------

Comment By: Nobody/Anonymous (nobody)
Date: 2009-04-09 00:17

Message:
(%i1) radcan(sqrt((x-1)^2));
(%o1)                             abs(x - 1)
(%i2) radcan(sqrt(x^2-2*x+1));
(%o2)                                x - 1
(%i3) build_info();
Maxima version: 5.17.1
Maxima build date: 19:10 12/18/2008
host type: i686-pc-mingw32
lisp-implementation-type: GNU Common Lisp (GCL)
lisp-implementation-version: GCL 2.6.8

----------------------------------------------------------------------

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