Question on writing a recurrence relation in C

[Guest_imported]

First of all, I'm an absolute beginner, so don't assume something is too obvious to say

Basically, I'm trying to write a program to evaluate, up to a given value of n, the recurrence relation:

y_n+1 = y_n-1 + 2*h*function(x_n,y_n)

Where _ denotes a subscript.

Ie. The current term is related to the previous term, and also the one before that.
(Here h is just a small constant, function() is a known function, and x_n+1 = x_n + h).

All the examples I have seen along these lines have been relating the current term with just the previous one (i=i+1 etc). How do I tell the program to use the one before that as well?

I hope this is just somthing simple that I don't know about, but I've been trying to work it out for a long time now and I'm completely stumped. I have to get past this in order to progress with my project, so any help at all would be very much appreciated.

Many thanks.

 

[CaKiwi]

Hi Dave,

This may get you started.

#define MAX 10
double function(double x, double y)
{
/* put your function calculation here */
  return ( ...);
}
main()
{
  double y[MAX],x,h;
  int i;
/* Initialize your variables here */
  h    = hval;
  x    = x-initial-value-1;
  y[0] = y-initial-value-0;
  y[1] = y-initial-value-1;

  for (i=1;i<MAX-1;y++)
  {
    x += h;
    y[i+1] = y[i-1] + 2*h*function(x,y[i]);
  }
}

CaKiwi

 

[Guest_imported]

Thanks very much!

That's a great help

Didn't know you could use arrays quite like that. I'll go try it.

Thanks again.