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rtoy / maxima

A Clone of Maxima's repo
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matrix(...taylor...)^^-1 wrong #3057

Open rtoy opened 4 months ago

rtoy commented 4 months ago

Imported from SourceForge on 2024-07-07 12:40:36 Created by macrakis on 2004-04-21 02:37:57 Original: https://sourceforge.net/p/maxima/bugs/561

Consider

m: matrix([taylor(1+a*x,x,0,1),0], [0,taylor(1+d*x,x,0,1)]);

Now,

m^^-1 => matrix([1/(d*x+1),0],[0,1/(d*x+1)])

There are two problems with this. First, the answer is incorrect. Compare:

matrixmap(ratdisrep,m)^^-1 => matrix([1/(a*x+1),0],[0,1/(d*x+1)])

Second, the answer is not in terms of taylor series. A silent ratdisrep was done in the middle, losing truncation information.

rtoy commented 4 months ago

Imported from SourceForge on 2024-07-07 12:40:37 Created by robert_dodier on 2006-04-09 20:43:44 Original: https://sourceforge.net/p/maxima/bugs/561/#fd9c