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Re: Initial condition with DSolve in Mathematica 8 doesn't work

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  • Subject: [mg116014] Re: Initial condition with DSolve in Mathematica 8 doesn't work
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sat, 29 Jan 2011 05:26:30 -0500 (EST)

The "Home Edition" has nothing to do with such a question. In (any 
edition of) Mathematica 8.0.0:

   DSolve[{y'[x] + y[x] == a Sin[x], y[0] == 0}, y[x], x] // InputForm
{{y[x] -> -(a*(-1 + E^x*Cos[x] - E^x*Sin[x]))/(2*E^x)}}

This is equivalent to what you obtained with Mathematica 7.0.1.

I suspect that before evaluating the DSolve expression in your 8.0.0 
session, you had set y[x] to be the solution, or something like that.


On 1/28/2011 6:14 AM, Bert RAM Aerts wrote:
> When I enter the following in Mathematica 8.0.0 Home Edition:
> DSolve[{y'[x] + y[x] == a Sin[x], y[0] == 0}, y[x], x]
> I get
> DSolve::deqn: Equation or list of equations expected instead of True
> in the first argument {y[x]+(y^\[Prime])[x]==a Sin[x],True}.>>
>
> The initial condition becomes a "True"...
>
> In Mathematica 7.0.1 Home Edition, this same input gives the expected
> output:
> {{y[x] ->  -(1/2) a E^-x (-1 + E^x Cos[x] - E^x Sin[x])}}
>
> What am I missing?
>

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
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University of Massachusetts                413 545-2859 (W)
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Amherst, MA 01003-9305


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