Re: DSOLVE in 5.01 ??
- To: mathgroup at smc.vnet.net
- Subject: [mg47584] Re: DSOLVE in 5.01 ??
- From: drbob at bigfoot.com (Bobby R. Treat)
- Date: Fri, 16 Apr 2004 05:21:46 -0400 (EDT)
- References: <c5j82s$r3h$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Here's a solution (for real constants):
Block[{v, result, eq},
eq = m g - c v[t]^2 == m v'[t];
v[t_] = Sqrt@u[t];
result = First@DSolve[eq, u[t], t];
Clear[v];
v[t_] = Sqrt@u[t] /. result;
Simplify[PowerExpand /@ {v[t], eq}]
]
Bobby
turbo cyx <turbocyx at gmx.net> wrote in message news:<c5j82s$r3h$1 at smc.vnet.net>...
> Hi
> The following sequnece worked fine in all Mathematica versions including 4.2
>
> dgl1 = m g - c v[t]^2 == m v'[t]
> dgl2 = s'[t] == -v[t]
> DSolve[{dgl1, dgl2, s[0] == h0,v[0] == 0}, {s[t], v[t]}, t]
>
> But since 5.0 (and now in 5.01) there are only a error messages ?
> Whats wrong here, why can't 5.01 solve this thing when 4.2 can???
> OTOH: DSolve without the boundary conditions works fine (DSolve[{dgl1,
> dgl2}, {s[t], v[t]}, t]), and calculationg the Constants C[1], C[2] by
> "hand" (i.e. with Solve) also...
> Thanks for help
> Cyx