[Maxima-bugs] [ maxima-Bugs-2299224 ] unsimplified result from rectform

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Bugs item #2299224, was opened at 2008-11-16 16:47
Message generated for change (Comment added) made by crategus
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Category: None
Group: Includes proposed fix
>Status: Pending
>Resolution: Works For Me
Priority: 5
Private: No
Submitted By: Barton Willis (willisbl)
Assigned to: Nobody/Anonymous (nobody)
Summary: unsimplified result from rectform

Initial Comment:
(%i1) logarc : true;
(%o1) true

(%i2) rectform(log(x + %i * y));
(%o2) log(y^2+x^2)/2+%i*atan2(y,x)

(%i3) expand(%,0,0);
(%o3) log(y^2+x^2)/2+(log((%i*y)/x+1)-log(1-(%i*y)/x))/2

Also (%o3) is wrong for x = 0 and in the left half plane.


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>Comment By: Dieter Kaiser (crategus)
Date: 2009-11-30 01:05

Message:
As discussed on the mailing list, rectform sets the option variable logarc
to NIL to preserve the standard form x+%i*y for its result.

With Maxima 5.19post we get:

(%i4) rectform(log(x+%i*y));
(%o4) log(y^2+x^2)/2+%i*atan2(y,x)

logarc gives the following result, which no longer has the standard form
of rectform:

(%i5) logarc(%);
(%o5) log((%i*y+x)/sqrt(y^2+x^2))+log(y^2+x^2)/2

I think we can close this bug report. The first issue has gone. The result
of rectform is correct. The second issue is the expected behavior. rectform
returns a standard form, which might simplify further, when the user sets
the option variable logarc to TRUE.

Setting the status to pending and the resolution to "works for me".

Dieter Kaiser

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Comment By: Dieter Kaiser (crategus)
Date: 2009-05-08 22:45

Message:
The expression does not simplify as expected because the global flag
$logarc is set to nil in the routine risplit. It is possible to remove this
from the routine risplit. Then we would get:

(%i11) rectform(log(x+%i*y)),logarc;
(%o11) log((%i*y+x)/sqrt(y^2+x^2))+log(y^2+x^2)/2

Because of revision 1.25 the result of the simplification is now correct.

I have checked this with the testsuite and the share_testsuite. There are
no examples which depend on the setting of $logargs in the routine
risplit.

Should we change the routine risplit and remove the setting of the flag
$logarg?

Dieter Kaiser

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