using System;
public static partial class matlib{

public static int binsearch(double[] x, double z)
	{/* locates the interval for z by bisection */ 
	if(!(x[0]<=z && z<=x[x.Length-1])) throw new Exception("binsearch: bad z");
	int i=0, j=x.Length-1;
	while(j-i>1){
		int mid=(i+j)/2;
		if(z>x[mid]) i=mid; else j=mid;
		}
	return i;
	}

public static double linterp(double[] x, double[] y, double z){
	int i=binsearch(x,z);
	double dx=x[i+1]-x[i]; if(!(dx>0))throw new Exception("uups...");
	double dy=y[i+1]-y[i];
	return y[i]+dy/dx*(z-x[i]);
	}

}