Services & ResourcesWolfram ForumsMathGroup Archive

[Date Index] [Thread Index] [Author Index]

Re: Bug in Homogeneous Solution of Differential equation?

• To: mathgroup at smc.vnet.net
• Subject: [mg132385] Re: Bug in Homogeneous Solution of Differential equation?
• From: Murray Eisenberg <murray at math.umass.edu>
• Date: Sun, 2 Mar 2014 21:28:14 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• Delivered-to: l-mathgroup@wolfram.com
• Delivered-to: mathgroup-outx@smc.vnet.net
• Delivered-to: mathgroup-newsendx@smc.vnet.net
• References: <20140302060632.D22236A01@smc.vnet.net>

I cannot understand what you mean by saying "select to solve as a 
homogeneous equation", given that this is a non-linear differential 
equation.

The correct Mathematica syntax is:

   DSolve[{y'[t] == y[t]/(y[t] - t), y[0] == 1}, y[t], t]

This provides solution

  {{y[t] -> t + Sqrt[1 + t^2]}}

along with warning that Inverse functions are being used, so some solutions may not be found.
On Mar 2, 2014, at 1:06 AM, amzoti <amzoti at gmail.com> wrote:

> I am using Mathematica V9.
>
> When I solve "= dy/dt = ( y )/ (y - t) , y(0) = 1" (using the WA approach within Mathematica), I get the correct answer.
>
> When I select "Solve as an exact equation" I also get the correct result.
>
> However, when I select to solve as a homogeneous equation, it leave the constant and does not appear ro converge.
>
> Is this a bug in step-by-step?
>
> Thanks -A
>


Murray Eisenberg                                murray at math.umass.edu
Mathematics & Statistics Dept.      
Lederle Graduate Research Tower      phone 240 246-7240 (H)
University of Massachusetts               
710 North Pleasant Street                
Amherst, MA 01003-9305

• References:
  • Bug in Homogeneous Solution of Differential equation?
    • From: amzoti <amzoti@gmail.com>