Possible Collect bug
- To: mathgroup at yoda.ncsa.uiuc.edu
- Subject: Possible Collect bug
- From: John Mitchell <uunet!pico.uchicago.edu!mitchell>
- Date: Mon, 20 Aug 90 17:48:34 CDT
I would like to relate a recent calculation I ran across which I believe
represents a bug in Mathematica 1.2.1 (Macintosh II version). I have
not seen this bug reported elsewhere, but it may have been. The sample
ouput below shows a comparison of Collect with Factor on what seems like
a straightforward expression. Note, however, that two different answers
result. I would appreciate anyone's comments on this.
(Note that this output has been "cut and pasted" from Mathematica
into a word-processing program before transfer, explaining the
missning In[##] and Out[##] )
expr = -((-1)^(2n) y^2)/8 - ((-1)^(-1 + 2n) y^2)/8 + ((-1)^(1 + 2n) y^2)/8
2 n 2 -1 + 2 n 2 1 + 2 n 2
-((-1) y ) (-1) y (-1) y
------------- - ----------------- + -----------------
8 8 8
Collect[expr,y]
2 n 2
-3 (-1) y
-------------
8
(* This is incorrect *)
Factor[expr]
2 n 2
-((-1) y )
-------------
8
(* This is correct *)
*****************************
John Mitchell
Univ. of Chicago
5735 South Ellis Ave.
Chicago, IL 60637
(312) 702-7253
mitchell at pico.uchicago.edu