d2r1f.java

用JAVA写的数值计算方法中的拉格朗日插值算法的程序

public class d2r1F
{
	public double  _x;
	public double  _y;
	public double  _dy;
	void polint (double xa[],double ya[],int n,double x,double y,double dy)
	{
		double c[]=new double[11];
		double d[]=new double[11];
		double dift,dif,ho,hp,w,den;
		int i,m,ns=1;
		dif=Math.abs(x-xa[1]);
		for(i=1 ;i<=n; i++)
		{
			dift=Math.abs(x-xa[i]);
			if(dift<dif)
			{
				ns=i;
				dif=dift;
				
			}
			c[i]=ya[i];
			d[i]=ya[i];
			
		}
		y=ya[ns];
		ns=ns-1;
		for(m=1; m<=n-1; m++)
		{
			for(i=1; i<=n-m; i++)
			{
				ho=xa[i]-x;
				hp=xa[i+m]-x;
				w=c[i+1]-d[i];
				den=ho-hp;
				if(den==0.0)
				{
					System.out.println("pause");
					return;
					
				}
				den=w/den;
				d[i]=hp*den;
				c[i]=ho*den;	
			}
			if(2*ns<n-m)
			   dy=c[ns+1];
			else
			{
				dy=d[ns];
				ns=ns-1;
				
			}
			y=y+dy;
		}
		 _x=x; _y=y; _dy=dy;
	}
}