Re: PSE Example 8.6 via Reduce

*To*: mathgroup at smc.vnet.net*Subject*: [mg112881] Re: PSE Example 8.6 via Reduce*From*: Daniel Lichtblau <danl at wolfram.com>*Date*: Tue, 5 Oct 2010 05:31:34 -0400 (EDT)

Eduardo Cavazos wrote: > On Sep 26, 1:44 am, Eduardo Cavazos <wayo.cava... at gmail.com> wrote: > >> Here's example 8.6 from PSE [1]: >> >> http://i.imgur.com/HJLqs.png >> >> Here I'll be working with the "exercise" portion of the example; i.e. >> the case where there is friction between point A and point B. >> >> Use Reduce on the set of equations which describe the system between >> point A and point B: >> >> http://i.imgur.com/PLWza.png >> >> The result shows that vB is about 12.9. >> >> Now use Reduce on the set of equations which describe the system >> between point B and point C. Also, plug in our value of 'vB' manually: >> >> http://i.imgur.com/rujUz.png >> >> We get the correct answer for dBC; i.e. about 40.3. >> >> Above I solved the problem in "piecemeal" fashion; first I used Reduce >> on the system from A to B and used the result from that to work with >> the system from B to C, also using Reduce. >> >> I don't have alot of experience with Reduce, but it seems like, in >> theory, I should be able to throw the whole set of equations at Reduce >> in one step, instead of in two steps. However, when I try to do so, >> Mathematica seems to have trouble with it (at least on this system; >> Pentium M with about 1.5GB RAM). So something along the lines of: >> >> http://i.imgur.com/2swfE.png >> >> So my questions are... Is this too much for Reduce to handle? Would >> you recommend the piecemeal method instead? > > In particular, the trouble is that the computation ran over 3 hours > without completing. When I split up the problem, each piece takes a > few seconds. > > Ed I do not know if you will get serious responses if you provide the code you used. But I rather suspect you will not get such responses in the absence of said code. Daniel Lichtblau Wolfram Research