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MathGroup Archive 1995

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Re: NDSolve problem

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg912] Re: NDSolve problem
  • From: saarinen (Sirpa Saarinen)
  • Date: Sun, 30 Apr 1995 03:46:37 -0400
  • Organization: Wolfram Research, Inc.

In <3nkcth$n02 at news0.cybernetics.net> pitts at mayo.EDU (Todd Pitts) writes:

>Changing the coefficient 4.0 in eq to unity (1 not 1.0) gives no error.  Also
>writing the equation as

>eq={D[x[1][t],{t,2}]==(x[1][t]-Sin[t])/4};

>works.  If I don't use subscripted variables I don't have this problem.  For
>example 

>sys2 = sys /. x[1] -> x
>NDSolve[sys2,x,{t,0,10}]

>seems to work fine.  I would greatly appreciate any hints.  Is this a bug or
>have I misunderstood the use of subscripted variables?  The version number is
>2.2.  I get the same behavior on NeXT and DEC Alfa.

The current version V2.2 of NDSolve does not support indexed variables,
so you could use something like 

Out[6]= {x''[t] == -Sin[t] + x[t], x'[0] == 0, x[0] == 0}

In[7]:= In[7]:= NDSolve[sys,x,{t,0., 10.}]


Out[7]= {{x -> InterpolatingFunction[{0., 10.}, <>]}}

In the version under development most N* functions in mathematica will
be supporting also indexed variables.



Sirpa Saarinen
saarinen at wri.com



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