Re: Calling lsode directly from a c++ program via liboctave?

[Douglas Eck]

Andrei Romanenko wrote:

> Hello!
>
> Great job! I was wondering if there is a quick way to supply parameters
> to the ode function. It seems Octave leaves us nothing but declare them
> as global. I am afraid it would be a pain to access global variables
> from an .oct file (symbol table lookups and stuff like that)...
> Have you discovered a better way to do that?


Yes. If you write xdot=f(x,t) in c++ instead of in octave,
it's simply a matter of using a static variable.

Here is my "f" function stripped from a current project:
ColumnVector lbBeatTracker::odeHelper (const ColumnVector& x, double t)
{
  //This is the function called multiple times by lsode.
  //Each oscillator has a voltage v and recovery w
  //These are concatinated such that x=[v1,v2,...,vk,w1,w2,...,wk]
  //The parameter epsilon controls the rate of oscillaton
  //it is stored in a static column vector epsilons
  for (int i=0;i<odeOscCount;i++) {
    odeXDot(i) = -x(i)*(x(i)-ODE_FITZ_THOLD) * (x(i)-1.0) - x(i+odeOscCount) + 
ODE_FITZ_CVOLT + odeSignal(i);
    odeXDot(i+odeOscCount) = odeEpsilons(i) * (x(i)-ODE_FITZ_SHUNT * 
x(i+odeOscCount));
  }
  return odeXDot;
}


Here are the definitions of the variables and constants from the accompanying
header file:
#define ODE_FITZ_THOLD .2
#define ODE_FITZ_CVOLT .112
#define ODE_FITZ_SHUNT 1.2
#define ODE_PTS_PER_SLICE 2

static ColumnVector odeEpsilons;      //epsilons
static ColumnVector odeSignal;        //signal
static ColumnVector odeXDot;          //return value
static int odeOscCount;               //oscillator count


You can write to these static variables before calling the
solver. Hope this helps.

Cheers,
Doug



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