FindInterval.c File Reference

Find grid point indices corresponding to a spatial interval. More...

#include <mathfunctions.h>

Go to the source code of this file.

Functions
void	FindInterval (double a, double b, double *x, int N, int *imin, int *imax)

Detailed Description

Find grid point indices corresponding to a spatial interval.

Author

Debojyoti Ghosh

Definition in file FindInterval.c.

Function Documentation

FindInterval()

void FindInterval	(	double	a,
		double	b,
		double *	x,
		int	N,
		int *	imin,
		int *	imax
	)

Given an interval \(\left[a,b\right], a\leq b\), find grid indices imin and imax, such that

\begin{align} imin &= \min\ i\ {\rm satisfying}\ x_i \geq a\\ imax &= \max\ i\ {\rm satisfying}\ x_i \leq b \end{align}

where \(\left\{x_i; 0\leq i < N , x_i < x_{i+1} \forall i \right\}\) represents a 1-dimensional grid.

Note: This function handles 1-dimensional intervals and grids only.

Parameters

a	Lower bound of interval
b	Upper bound of interval
x	Array of spatial coordinates representing a grid
N	Number of grid points / size of x
imin	Lowest grid index within [a,b]
imax	Highest grid index within [a,b]

Definition at line 19 of file FindInterval.c.

{
  int i;
  *imax = -1;
  *imin =  N;

  double min_dx = x[1] - x[0];
  for (i = 2; i < N; i++) {
    double dx = x[i] - x[i-1];
    if (dx < min_dx) min_dx = dx;
  }
  double tol = 1e-10 * min_dx;

  for (i = 0; i < N; i++) {
    if (x[i] <= (b+tol)) *imax = i+1;
  }
  for (i = N-1; i > -1; i--) {
    if (x[i] >= (a-tol)) *imin = i;
  }

  return;
}