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MathGroup Archive 2007

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Re: Re: Solving differential equations with parameters

  • To: mathgroup at smc.vnet.net
  • Subject: [mg79826] Re: [mg79822] Re: Solving differential equations with parameters
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Mon, 6 Aug 2007 03:33:29 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

Use Part or Flatten to remove the undesired brace

sol = y /. NDSolve[{y'[x] == 1/2 y[x], y[0.01] == 0.1}, y, {x, 0.01, 1}][[1]];

You need to add in the x-coordinate to get anything useful from the Plot

g = Table[{i, sol[i]}, {i, 0.01, 1, 0.01}];

ListPlot[g]

However, you can Plot an InterpolatingFunction without building a Table.

Plot[sol[x], {x, 0.01, 1}]


Bob Hanlon

---- Ivan <darknails at gmail.com> wrote: 
> On Aug 4, 12:07 pm, Ivan <darkna... at gmail.com> wrote:
> > Hi, I am trying to solve the differential equations like
> >
> > y'[x]= - Sin[ p*x + y[x] ]
> >
> > where p is a parameter. Now I want to solve the equation with respect
> > to x for a range of values of p, instead for just a single p.
> > What is the best way to do it?
> 
> I now have a way to do it but there is another problem..
> 
> I use the Table command (I change the function for the sake of
> demonstration)
> 
> sol = NDSolve[{y'[x]==1/2y[x],y[0.01]==0.1}, y, {x, 0.01,1}];
> 
> g=Table[ {y[i*0.01]/.sol}, {i,100} ];
> 
> ListPlot[g];
> 
> The error message is gptn: Coordindate .. in ... is not a floating-
> point number.
> 
> The problem seems to be that y[x]/.sol generate not a "normal" number,
> instead, the number is is a brace {...}.
> 
> Can anyone help me?
> 
> 



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