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Re: How to pass output of one lsode as input to other lsode at a given t

From: Juan Pablo Carbajal
Subject: Re: How to pass output of one lsode as input to other lsode at a given time step
Date: Tue, 24 Feb 2015 00:32:43 +0100

On Mon, Feb 16, 2015 at 12:19 PM, scjoshi
<address@hidden> wrote:
> Hello All,
> I have a set of two ODE in which output of one has to be passed on as input
> to the other.
> Say the first ODE is:
> xdot = f1(x,t) whose outputs are x(1), x(2) and x(3). These are to be passed
> on as inputs to other ODE....
> say
> ydot = f2(y,t,x(1),x(2),x(3))
> Both these equations are to be solved simultaneously.
> Any examples would be appreciated.
> --
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> address@hidden

What you have is a coupled system of equations and one way to solve it
is to create a bigger system and solve it with lsode.

Something like (pseudo-code)

function dx = bigSYS(x,t)
  [dx(1),dx(2),dx(3)] = f1(x(1:3),t)
  [dx(4),dx(5),dx(6)] = f2(x,t);

You have to realize that the current output of the system of ODEs
comes in the input vector x.

If, however, your second ODE, is not really an "ODE" but is a
functional of the solution trajectory of your first ODE, more details
are needed to now how to express the whole system as an ODE...if

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