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Taylor series of sqrt(1+x-y) #3245

Open rtoy opened 4 months ago

rtoy commented 4 months ago

Imported from SourceForge on 2024-07-07 18:42:39 Created by *anonymous on 2008-10-28 03:36:06 Original: https://sourceforge.net/p/maxima/bugs/1517

Taylor expansion results of f:sqrt(1+x-y) depends on sequence: (1) taylor(f,y,0,1); taylor(%,x,0,1) works properly: 1-y/2+...+(1/2+y/4+...)*x+... (2) taylor(f,x,0,1); taylor(%,y,0,1) generates bad results: -1-x/2+...+(1/2+x/4+...)*y+... The square of the "bad result" is 1+x-y, but it is not the narrow definition of sqrt(), which should be positive in this case.

rtoy commented 4 months ago

Imported from SourceForge on 2024-07-07 18:42:39 Created by boud1 on 2009-02-19 02:32:46 Original: https://sourceforge.net/p/maxima/bugs/1517/#3aad

This bug is IMHO related to

[ 2184396 ] Wrong factorization of sqrt() Submitted By: Satoshi Adachi - satoshi_adachi
Date Submitted: 2008-10-21 13:05 http://sourceforge.net/tracker/index.php?func=detail&aid=2184396&group\_id=4933&atid=104933

A hack solution is: radexpand : false; See 218439 for more discussion.