samer@0: /*
samer@0:  *	Copyright (c) 2000, Samer Abdallah, King's College London.
samer@0:  *	All rights reserved.
samer@0:  *
samer@0:  *	This software is provided AS iS and WITHOUT ANY WARRANTY; 
samer@0:  *	without even the implied warranty of MERCHANTABILITY or 
samer@0:  *	FITNESS FOR A PARTICULAR PURPOSE.
samer@0:  */
samer@0: 
samer@0: package samer.maths.opt;
samer@0: 
samer@0: /**
samer@0: 	This is a function interface that is designed
samer@0: 	to allow efficient implementations of minimisation
samer@0: 	algorithms by recognising the fact that the
samer@0: 	function and its gradient may be repeatedly 
samer@0: 	evaluated at the same point in different parts
samer@0: 	of the code - hence we can save ourselves
samer@0: 	some computation.
samer@0: 
samer@0:  */
samer@0: 
samer@0: 
samer@0: public class SubspaceFunctionx implements Functionx
samer@0: {
samer@0: 	Functionx	fn;	// underlying function
samer@0: 	Datum			P;		// Datum big enough for fn
samer@0: 	int []		k;		// small array of indices into big space
samer@0: 	int			m;
samer@0: 
samer@0: 	public SubspaceFunctionx(Functionx fn, int n, int m) {
samer@0: 		this.fn=fn;
samer@0: 		this.m=m;
samer@0: 		P=new Datum(n);
samer@0: 		k=new int[m];
samer@0: 	}
samer@0: 
samer@0: 	/** means ith coor in little space maps to jth coor in big space */
samer@0: 	public void setMap(int i, int j) { k[i]=j; }
samer@0: 	public double[] getX() { return P.x; }
samer@0: 	
samer@0: 	/** get value and gradient for supplied point */
samer@0: 	public void evaluate( Datum P) {
samer@0: 		projectUp(P.x, this.P.x);
samer@0: 		fn.evaluate(this.P);
samer@0: 		P.f=this.P.f;
samer@0: 		projectDown(this.P.g,P.g);
samer@0: 	}
samer@0: 
samer@0: 	/** set argument to x, return value and put gradient in dx */
samer@0: 	public double evaluate( double [] x, double [] g) {
samer@0: 		projectUp(x,P.x);
samer@0: 		P.f=fn.evaluate(P.x,P.g);
samer@0: 		projectDown(P.g,g);
samer@0: 		return P.f;
samer@0: 	}
samer@0: 
samer@0: 	protected void projectUp(double [] a, double [] b) {
samer@0: 		for (int i=0; i<m; i++) b[k[i]]=a[i];
samer@0: 	}
samer@0: 	
samer@0: 	protected void projectDown(double [] a, double [] b) {
samer@0: 		for (int i=0; i<m; i++) b[i]=a[k[i]];
samer@0: 	}
samer@0: 
samer@0: 	public void dispose() { P.dispose(); fn.dispose(); }
samer@0: }