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MathGroup Archive 1993

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NDSolve

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: NDSolve
  • From: Erlebacher Gordon <erlebach at icase.edu>
  • Date: Fri, 22 Oct 93 09:27:26 -0400

I have a problem with the routine NDSolve.  Spefically, I am trying 
to solve the differential equation:

  y'[x] = 3 y[x]

  y[0] =  1

using the command  NDSolve.  Here is a transcript of my session:

----------------------------------------------------------------------

In[1]:= NDSolve[{y'[x] == 3 y[x],y[0] == 1},y,{x,0,3}]

Out[1]= {{y -> InterpolatingFunction[{0., 3.}, <>]}}

----------------------------------------------------------------------
What is this InterpolatingFunction.  Let us try another equation:

   y'[x] = 5 x y[x]

   y[0] = 2

----------------------------------------------------------------------

In[3]:=  NDSolve[{y'[x] == 5 x y[x],y[0] ==2}, y,{x,0,3}]

Out[3]= {{y -> InterpolatingFunction[{0., 3.}, <>]}}

----------------------------------------------------------------------
Note that the InterpolatingFunction is the same in both cases, yet the
equation is different.


Now how do I retrieve a list of numbers from this InterpolatingFunction[]
routine?  What I really would like to do is subtract the second solution
from the first, and retrieve the value at the end points.


   Thanks in advance,

	 Gordon Erlebacher
	 ICASE, NASA Langley Research Center





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