Re: Interesting failure of Collect
- To: mathgroup at smc.vnet.net
- Subject: [mg61343] Re: [mg61307] Interesting failure of Collect
- From: "David Park" <djmp at earthlink.net>
- Date: Sun, 16 Oct 2005 00:17:58 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Jerry, It looks like a bug but it is probably an unintuitive feature from trying to extend the Collect patterns to include numbers. Pi seems to be permitted but the 1/4 causes the problem. You may be able to overcome the problem by omitting numbers and including FactorTerms as the last argument in Collect. Collect[expr, Sin[p]/Pi, FactorTerms] ((1/a + 1/b)*Sin[p])/(4*Pi) Collect[expr2, Sin[p]/Pi, FactorTerms] ((1/a - 1/b)*Sin[p])/(4*Pi) The last argument to Collect is easy to overlook and is often quite useful. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Blimbaum, Jerry CIV NSWC PC [mailto:jerry.blimbaum at navy.mil] To: mathgroup at smc.vnet.net Given the expr = Sin[p]/(4 Pi a) + Sin[p]/(4 Pi b) and then applying the command Collect[expr, Sin[p]/(4 Pi)] works as it should, however, expr2 = Sin[p]/(4 Pi a) - Sin[p]/(4 Pi b) leaves the expression untouched. (I realize I could use Simplify but this problem occurred on a much longer expression and this is intended just to convey the basic idea)....for longer expressions the Collect process works for all quantities with a + sign but the one with a minus sign will not be collected.....strikes me as a "bug"..... thanks....jerry blimbaum