[Maxima-bugs] [ maxima-Bugs-1928142 ] keepfloat breaks ratsubst() in some cases

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Bugs item #1928142, was opened at 2008-03-28 18:37
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Category: Lisp Core - Simplification
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Harald Geyer (hgeyer)
Assigned to: Nobody/Anonymous (nobody)
Summary: keepfloat breaks ratsubst() in some cases

Initial Comment:
ratsubst returns incorrect results when keepfloat==true and the substitution causes the expression to contain both floats and rationals at the same time. See the following example session for things that don't work as well as for some things that do work.

I can reproduce the problem from at least 5.11.0 up to current cvs with clisp and gcl.

Maxima 5.14.0cvs http://maxima.sourceforge.net
Using Lisp CLISP 2.41 (2006-10-13)
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(ratsubstbug.mac)

batching /home/rld/ratsubstbug.mac
(%i2)                          keepfloat : true
(%i3)                          display2d : false
(%i4) cos(%pi/3)
(%o4) 1/2
(%i5) subst(%pi/3,th,1.2*cos(th))
(%o5) 0.6
(%i6) ratsubst(%pi/3,th,1.2*cos(th))
(%o6) 1.2
(%i7) cos(%pi)
(%o7) -1
(%i8) subst(%pi,th,1.2*cos(th))
(%o8) -1.2
(%i9) ratsubst(%pi,th,1.2*cos(th))
(%o9) -1.2
(%i10) sqrt(1/4)
(%o10) 1/2
(%i11) subst(4,th,1.2*sqrt(1/th))
(%o11) 0.6
(%i12) ratsubst(4,th,1.2*sqrt(1/th))
Maxima encountered a Lisp error:

 
COMMON-LISP:GCD: 1.2 is not an integer

Automatically continuing.
To reenable the Lisp debugger set *debugger-hook* to nil.
(%i13) subst(9,th,1.2*sqrt(1/th))
(%o13) 0.4
(%i14) ratsubst(9,th,1.2*sqrt(1/th))
Maxima encountered a Lisp error:

 
COMMON-LISP:GCD: 1.2 is not an integer

Automatically continuing.
To reenable the Lisp debugger set *debugger-hook* to nil.
(%i15) ratsubst(9,th,1.2*sqrt(th))
(%o15) 3.6
(%i16) ratsubst(4,th,1.2/sqrt(th))
Maxima encountered a Lisp error:

 
COMMON-LISP:GCD: 1.2 is not an integer

Automatically continuing.
To reenable the Lisp debugger set *debugger-hook* to nil.
(%i17) log(%e^(1/2))
(%o17) 1/2
(%i18) subst(%e^(1/2),th,1.2*log(th))
(%o18) 0.6
(%i19) ratsubst(%e^(1/2),th,1.2*log(th))
(%o19) 1.2
(%i20) ratsubst(%e^(1/3), th, 1.2*log(th));
(%o20) 1.2
(%i21) subst(%e^2,th,1.2*log(th))
(%o21) 2.4
(%i22) ratsubst(%e^2,th,1.2*log(th))
(%o22) 2.4


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