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Re: Plot using DSolve HELP
*To*: mathgroup at smc.vnet.net
*Subject*: [mg104418] Re: [mg104388] Plot using DSolve HELP
*From*: Bob Hanlon <hanlonr at cox.net>
*Date*: Sat, 31 Oct 2009 01:50:51 -0500 (EST)
*Reply-to*: hanlonr at cox.net
Your eq is not an equation, it is an expression. I don't know how you got a result from DSolve
eq = i*v[t]/r + c v'[t] == -2/5;
Use exact numbers with DSolve
sol[t_] = v[t] /. DSolve[{eq /. {c -> 3, i -> 0, r -> 5/2},
v[0] == -70}, v[t], t][[1]]
-(2/15) (t+525)
Plot[sol[t], {t, -20, 140}]
Bob Hanlon
---- Becky <noslowski at comcast.net> wrote:
=============
I have a problem with what I am showing below.
Step one is my equation.
eq = i * v[t]/r +c v'[t]
Step two I want to solve it, using DSolve, and put my values in as shown.
Please note, that "i= 0", and my IC is v[0]== -70.
sol=v[t]/.DSolve[{eq/.{c->3, i->0, r->2.5} ,v[0]==-70}, v[t], t]
{-70 *-0.133333 t}
The results are shown above.
Thus next step is to plot it.
p1=Plot[sol,{t,-20,140}]
My problem is that I get a line from -70 on the vertical axis going in a
curve up to the horizontal axis out to 140. The vertical axis is "v" and
the horizontal is "t".
What am I doing wrong?
Thanks
Jake
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