Re: Getting the value of the independent var from the dep.var using NDSolve
- To: mathgroup at smc.vnet.net
- Subject: [mg63684] Re: Getting the value of the independent var from the dep.var using NDSolve
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Tue, 10 Jan 2006 01:48:39 -0500 (EST)
- Organization: The Open University, Milton Keynes, UK
- References: <dptd4r$be$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
pradeep suresh wrote:
> Hi all,
> i have a specific problem of finding the point at which the dependent
> variable takes on a particular value in teh solution of a differential
> equation.
> e.g. for simplicity
> we have the equation y'[t]==t, and the initial cond. y[0]==0.y is the
> dep. variable and t is the independent variable.
> i want to find out the 't' at which y[t]==p(p is known, say 8)
> and since i am already using NDSolve to solve this and other equations
> i'd like to achieve this working around NDSolve,
> could anyone suggets a solution to this problem??
> thanks a ton!
> Pradeep
>
Hi Pradeep,
Is something like the following lines may help you?
In[1]:=
sol=NDSolve[{y'[t]\[Equal]t,y[0]\[Equal]0}, y, {t, 0, 10}]
Out[1]=
{{y\[Rule]InterpolatingFunction[{{0.,10.}},<>]}}
In[2]:=
FindRoot[Evaluate[y[t]/.sol[[1,1]]]\[Equal]8,{t,7}]
Out[2]=
{t\[Rule]4.}
In[3]:=
y[4]/.sol[[1,1]]
Out[3]=
8.
Best regards,
/J.M.