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Topic: Result to DEQ with WA versus Step-by-Step Yields
Replies: 5   Last Post: Feb 8, 2014 3:47 AM

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amzoti

Posts: 1,108
Registered: 3/6/07
Re: Result to DEQ with WA versus Step-by-Step Yields
Posted: Feb 7, 2014 1:24 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

On Saturday, February 1, 2014 8:44:33 PM UTC-8, Bob Hanlon wrote:
> The step-by-step solution provides the result for t >= 0
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> sol = ((WolframAlpha[
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> "v''+10 v'+125 v=250 unitstep(t),v(0)=0,v'(0)=25",
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> {{"DifferentialEquationSolution", 1}, "Output"}] //
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> ReleaseHold)[[1]]) // ToRules
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> {v[t] -> ((5/2)*Sin[10*t])/E^(5*t) +
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> (((-(5/2))*Sin[10*t])/E^(5*t) +
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> ((1/2)*(4*E^(5*t) - 4*Cos[10*t] + 3*Sin[10*t]))/
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> E^(5*t))*UnitStep[t]}
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> Simplify[sol, t >= 0]
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> {v[t] -> 2 - (2*Cos[10*t])/E^(5*t) +
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> ((3/2)*Sin[10*t])/E^(5*t)}
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> Bob Hanlon
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> On Sat, Feb 1, 2014 at 12:54 AM, amzoti <amzoti@gmail.com> wrote:
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> > When you solve this DEW using WA, you get a result.
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> >
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> > However, when you click step-by-step, the result is different.
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> >
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> > Is this a bug?
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> >
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> > v'' + 10 v' + 125 v = 250 unitstep(t), v(0) = 0, v'(0) = 25
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> >
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> > Thanks
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> >
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> >

Thanks all!

Bob Hanlon: I see that you reply to many posting with excellent feedback.

I have always wondered (as your posts are different than many in a very good way), how did you learn Mathematica so well?

What approach and/or references did you use?

Regards -A




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