Re: DSolve Question

*To*: mathgroup at smc.vnet.net*Subject*: [mg50615] Re: DSolve Question*From*: "John Reed" <nospamjreed at alum.mit.edu>*Date*: Mon, 13 Sep 2004 02:19:30 -0400 (EDT)*References*: <200409111044.GAA19893@smc.vnet.net> <ci12e0$1e5$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Thanks for bringing up the bug suggestion. There is documentation about this problem on the Mathematica site at: http://support.wolfram.com/mathematica/mathematics/equations/dsolveproblem.html I was able to solve the problem using this method. John Reed "Selwyn Hollis" <sh2.7183 at misspelled.erthlink.net> wrote in message news:ci12e0$1e5$1 at smc.vnet.net... > > On Sep 11, 2004, at 6:44 AM, John Reed wrote: > >> I'm relatively new to Mathematica, and I'm having trouble with a >> simple DE. >> This is from Zimmerman & Olness, "Mathematica for Physics". Here's the >> equation: >> >> eq1 = y''[t] + w^2 y[t] == 0 >> >> initial = {y[0] == y0, y'[0] == v0} >> >> eq3 = DSolve[{eq1, initial}, y[t], t] >> >> When this executes, I get the error message bvnul: For some branches >> of the >> general solution, the given boundary conditions lead to an empty >> solution. >> >> Now, if I change v0 to a number, everything works fine. I've tried >> making >> v0 real and positive, but with no luck. >> >> Any help is appreciated. >> >> John Reed > > > Hi John, > > You've rediscovered a "bug" in DSolve that's new in 5.0. Here's one > workaround: > > eq1 = y''[t] + w^2 y[t] == 0 > > initial = {y[0] == y0, y'[0] == v0} > > soln[t_] = y[t] /. First@DSolve[eq1, y[t], t] > > soln[t] /. First@Solve[initial /. y -> soln, {C[1], C[2]}] > > > > ----- > Selwyn Hollis > http://www.appliedsymbols.com > (edit reply-to to reply) >

**References**:**DSolve Question***From:*"John Reed" <nospamjreed@alum.mit.edu>