new DSolve feature

*To*: mathgroup at smc.vnet.net*Subject*: [mg46974] new DSolve feature*From*: Selwyn Hollis <sh2.7183 at misspelled.erthlink.net>*Date*: Thu, 18 Mar 2004 01:25:00 -0500 (EST)*References*: <c387p7$bij$1@smc.vnet.net> <200403170753.CAA16766@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

The following occurs in version 5.0.1 (Mac OS X). This works as expected: DSolve[x''[t] == -k x'[t] , x[t], t] {{x[t] -> -(C[1]/(E^(k*t)*k)) + C[2]}} So does this: DSolve[{x''[t] == -k x'[t], x[0] == x0, x'[0] == 1}, x[t], t] {{x[t] -> (-1 + E^(k*t) + E^(k*t)*k*x0)/(E^(k*t)*k)}} However: DSolve[{x''[t] == -k x'[t], x[0] == x0, x'[0] == v0}, x[t], t] DSolve::bvnul: For some branches of the general solution, the given boundary conditions lead to an empty solution. {} I wonder which "branches" of it are causing the difficulty. :^) ----- Selwyn Hollis http://www.math.armstrong.edu/faculty/hollis (edit reply-to to reply)

**References**:**Re: Exact real solutions of cubic equations***From:*Paul Abbott <paul@physics.uwa.edu.au>