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Re: problems with DSolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99423] Re: [mg99375] problems with DSolve
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Tue, 5 May 2009 05:43:52 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

Read the documentation for Plot and look at the numerous examples that use Evaluate.

Plot[Evaluate[x[t] /. DSolve[
    {x'[t] == y[t], y'[t] == -x[t], x[0] == 1, y[0] == 2},
    {x, y}, t]], {t, 0, 5}]


Bob Hanlon

---- szymon.stoma at gmail.com wrote: 

=============
hello,

i am new to mathematica, therefore sorry if my question is trivial. I
would like to understand why the following line does not work:

Plot[(x[t] /. DSolve[{x'[t] == y[t], y'[t] == -x[t], x[0] == 1, y[0]
== 2}, {x, y}, t]), {t, 0, 5}]

whereas after splitting into two lines it works:
sol = DSolve[{x'[t] == y[t], y'[t] == -x[t], x[0] == 1, y[0] == 2},
{x, y}, t]
Plot[(x[t] /. sol), {t, 0, 5}]

i would like to use Manipulate to play with boundary conditions, so
the first notation would be highly useful.

thanks a lot for any feedback.



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