/*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* Optimization.java
* Copyright (C) 2003-2012 University of Waikato, Hamilton, New Zealand
*
*/
package weka.core;
import weka.core.TechnicalInformation.Field;
import weka.core.TechnicalInformation.Type;
import weka.core.matrix.Matrix;
/**
* Implementation of Active-sets method with BFGS update to solve optimization
* problem with only bounds constraints in multi-dimensions. In this
* implementation we consider both the lower and higher bound constraints. <p/>
*
* Here is the sketch of our searching strategy, and the detailed description
* of the algorithm can be found in the Appendix of Xin Xu's MSc thesis:<p/>
* Initialize everything, incl. initial value, direction, etc.<p/>
* LOOP (main algorithm):<br/>
*
* 1. Perform the line search using the directions for free variables<br/>
* 1.1 Check all the bounds that are not "active" (i.e. binding variables)
* and compute the feasible step length to the bound for each of them<br/>
* 1.2 Pick up the least feasible step length, say \alpha, and set it as
* the upper bound of the current step length, i.e.
* 0<\lambda<=\alpha<br/>
* 1.3 Search for any possible step length<=\alpha that can result the
* "sufficient function decrease" (\alpha condition) AND "positive
* definite inverse Hessian" (\beta condition), if possible, using
* SAFEGUARDED polynomial interpolation. This step length is "safe" and
* thus is used to compute the next value of the free variables .<br/>
* 1.4 Fix the variable(s) that are newly bound to its constraint(s).<p/>
*
* 2. Check whether there is convergence of all variables or their gradients.
* If there is, check the possibilities to release any current bindings of
* the fixed variables to their bounds based on the "reliable" second-order
* Lagarange multipliers if available. If it's available and negative for
* one variable, then release it. If not available, use first-order
* Lagarange multiplier to test release. If there is any released
* variables, STOP the loop. Otherwise update the inverse of Hessian matrix
* and gradient for the newly released variables and CONTINUE LOOP.<p/>
*
* 3. Use BFGS formula to update the inverse of Hessian matrix. Note the
* already-fixed variables must have zeros in the corresponding entries
* in the inverse Hessian.<p/>
*
* 4. Compute the new (newton) search direction d=H^{-1}*g, where H^{-1} is the
* inverse Hessian and g is the Jacobian. Note that again, the already-
* fixed variables will have zero direction.<p/>
*
* ENDLOOP<p/>
*
* A typical usage of this class is to create your own subclass of this class
* and provide the objective function and gradients as follows:<p/>
* <pre>
* class MyOpt extends Optimization {
* // Provide the objective function
* protected double objectiveFunction(double[] x) {
* // How to calculate your objective function...
* // ...
* }
*
* // Provide the first derivatives
* protected double[] evaluateGradient(double[] x) {
* // How to calculate the gradient of the objective function...
* // ...
* }
*
* // If possible, provide the index^{th} row of the Hessian matrix
* protected double[] evaluateHessian(double[] x, int index) {
* // How to calculate the index^th variable's second derivative
* // ...
* }
* }
* </pre>
*
* When it's the time to use it, in some routine(s) of other class...
* <pre>
* MyOpt opt = new MyOpt();
*
* // Set up initial variable values and bound constraints
* double[] x = new double[numVariables];
* // Lower and upper bounds: 1st row is lower bounds, 2nd is upper
* double[] constraints = new double[2][numVariables];
* ...
*
* // Find the minimum, 200 iterations as default
* x = opt.findArgmin(x, constraints);
* while(x == null){ // 200 iterations are not enough
* x = opt.getVarbValues(); // Try another 200 iterations
* x = opt.findArgmin(x, constraints);
* }
*
* // The minimal function value
* double minFunction = opt.getMinFunction();
* ...
* </pre>
*
* It is recommended that Hessian values be provided so that the second-order
* Lagrangian multiplier estimate can be calcluated. However, if it is not
* provided, there is no need to override the <code>evaluateHessian()</code>
* function.<p/>
*
* REFERENCES (see also the <code>getTechnicalInformation()</code> method):<br/>
* The whole model algorithm is adapted from Chapter 5 and other related
* chapters in Gill, Murray and Wright(1981) "Practical Optimization", Academic
* Press. and Gill and Murray(1976) "Minimization Subject to Bounds on the
* Variables", NPL Report NAC72, while Chong and Zak(1996) "An Introduction to
* Optimization", John Wiley & Sons, Inc. provides us a brief but helpful
* introduction to the method. <p/>
*
* Dennis and Schnabel(1983) "Numerical Methods for Unconstrained Optimization
* and Nonlinear Equations", Prentice-Hall Inc. and Press et al.(1992) "Numeric
* Recipe in C", Second Edition, Cambridge University Press. are consulted for
* the polynomial interpolation used in the line search implementation. <p/>
*
* The Hessian modification in BFGS update uses Cholesky factorization and two
* rank-one modifications:<br/>
* Bk+1 = Bk + (Gk*Gk')/(Gk'Dk) + (dGk*(dGk)'))/[alpha*(dGk)'*Dk]. <br/>
* where Gk is the gradient vector, Dk is the direction vector and alpha is the
* step rate. <br/>
* This method is due to Gill, Golub, Murray and Saunders(1974) ``Methods for
* Modifying Matrix Factorizations'', Mathematics of Computation, Vol.28,
* No.126, pp 505-535. <p/>
*
* @author Xin Xu (xx5@cs.waikato.ac.nz)
* @version $Revision: 8076 $
* @see #getTechnicalInformation()
*/
public abstract class Optimization
implements TechnicalInformationHandler, RevisionHandler {
protected double m_ALF = 1.0e-4;
protected double m_BETA = 0.9;
protected double m_TOLX = 1.0e-6;
protected double m_STPMX = 100.0;
protected int m_MAXITS = 200;
protected static boolean m_Debug = false;
/** function value */
protected double m_f;
/** G'*p */
private double m_Slope;
/** Test if zero step in lnsrch */
protected boolean m_IsZeroStep = false;
/** Used when iteration overflow occurs */
protected double[] m_X;
/** Compute machine precision */
protected static double m_Epsilon, m_Zero;
static {
m_Epsilon=1.0;
while(1.0+m_Epsilon > 1.0){
m_Epsilon /= 2.0;
}
m_Epsilon *= 2.0;
m_Zero = Math.sqrt(m_Epsilon);
if (m_Debug)
System.err.print("Machine precision is "+m_Epsilon+
" and zero set to "+m_Zero);
}
/**
* Returns an instance of a TechnicalInformation object, containing
* detailed information about the technical background of this class,
* e.g., paper reference or book this class is based on.
*
* @return the technical information about this class
*/
public TechnicalInformation getTechnicalInformation() {
TechnicalInformation result;
TechnicalInformation additional;
result = new TechnicalInformation(Type.MASTERSTHESIS);
result.setValue(Field.AUTHOR, "Xin Xu");
result.setValue(Field.YEAR, "2003");
result.setValue(Field.TITLE, "Statistical learning in multiple instance problem");
result.setValue(Field.SCHOOL, "University of Waikato");
result.setValue(Field.ADDRESS, "Hamilton, NZ");
result.setValue(Field.NOTE, "0657.594");
additional = result.add(Type.BOOK);
additional.setValue(Field.AUTHOR, "P. E. Gill and W. Murray and M. H. Wright");
additional.setValue(Field.YEAR, "1981");
additional.setValue(Field.TITLE, "Practical Optimization");
additional.setValue(Field.PUBLISHER, "Academic Press");
additional.setValue(Field.ADDRESS, "London and New York");
additional = result.add(Type.TECHREPORT);
additional.setValue(Field.AUTHOR, "P. E. Gill and W. Murray");
additional.setValue(Field.YEAR, "1976");
additional.setValue(Field.TITLE, "Minimization subject to bounds on the variables");
additional.setValue(Field.INSTITUTION, "National Physical Laboratory");
additional.setValue(Field.NUMBER, "NAC 72");
additional = result.add(Type.BOOK);
additional.setValue(Field.AUTHOR, "E. K. P. Chong and S. H. Zak");
additional.setValue(Field.YEAR, "1996");
additional.setValue(Field.TITLE, "An Introduction to Optimization");
additional.setValue(Field.PUBLISHER, "John Wiley and Sons");
additional.setValue(Field.ADDRESS, "New York");
additional = result.add(Type.BOOK);
additional.setValue(Field.AUTHOR, "J. E. Dennis and R. B. Schnabel");
additional.setValue(Field.YEAR, "1983");
additional.setValue(Field.TITLE, "Numerical Methods for Unconstrained Optimization and Nonlinear Equations");
additional.setValue(Field.PUBLISHER, "Prentice-Hall");
additional = result.add(Type.BOOK);
additional.setValue(Field.AUTHOR, "W. H. Press and B. P. Flannery and S. A. Teukolsky and W. T. Vetterling");
additional.setValue(Field.YEAR, "1992");
additional.setValue(Field.TITLE, "Numerical Recipes in C");
additional.setValue(Field.PUBLISHER, "Cambridge University Press");
additional.setValue(Field.EDITION, "Second");
additional = result.add(Type.ARTICLE);
additional.setValue(Field.AUTHOR, "P. E. Gill and G. H. Golub and W. Murray and M. A. Saunders");
additional.setValue(Field.YEAR, "1974");
additional.setValue(Field.TITLE, "Methods for modifying matrix factorizations");
additional.setValue(Field.JOURNAL, "Mathematics of Computation");
additional.setValue(Field.VOLUME, "28");
additional.setValue(Field.NUMBER, "126");
additional.setValue(Field.PAGES, "505-535");
return result;
}
/**
* Subclass should implement this procedure to evaluate objective
* function to be minimized
*
* @param x the variable values
* @return the objective function value
* @throws Exception if something goes wrong
*/
protected abstract double objectiveFunction(double[] x) throws Exception;
/**
* Subclass should implement this procedure to evaluate gradient
* of the objective function
*
* @param x the variable values
* @return the gradient vector
* @throws Exception if something goes wrong
*/
protected abstract double[] evaluateGradient(double[] x) throws Exception;
/**
* Subclass is recommended to override this procedure to evaluate second-order
* gradient of the objective function. If it's not provided, it returns
* null.
*
* @param x the variables
* @param index the row index in the Hessian matrix
* @return one row (the row #index) of the Hessian matrix, null as default
* @throws Exception if something goes wrong
*/
protected double[] evaluateHessian(double[] x, int index) throws Exception{
return null;
}
/**
* Get the minimal function value
*
* @return minimal function value found
*/
public double getMinFunction() {
return m_f;
}
/**
* Set the maximal number of iterations in searching (Default 200)
*
* @param it the maximal number of iterations
*/
public void setMaxIteration(int it) {
m_MAXITS=it;
}
/**
* Set whether in debug mode
*
* @param db use debug or not
*/
public void setDebug(boolean db) {
m_Debug = db;
}
/**
* Get the variable values. Only needed when iterations exceeds
* the max threshold.
*
* @return the current variable values
*/
public double[] getVarbValues() {
return m_X;
}
/**
* Find a new point x in the direction p from a point xold at which the
* value of the function has decreased sufficiently, the positive
* definiteness of B matrix (approximation of the inverse of the Hessian)
* is preserved and no bound constraints are violated. Details see "Numerical
* Methods for Unconstrained Optimization and Nonlinear Equations".
* "Numeric Recipes in C" was also consulted.
*
* @param xold old x value
* @param gradient gradient at that point
* @param direct direction vector
* @param stpmax maximum step length
* @param isFixed indicating whether a variable has been fixed
* @param nwsBounds non-working set bounds. Means these variables are free and
* subject to the bound constraints in this step
* @param wsBdsIndx index of variables that has working-set bounds. Means
* these variables are already fixed and no longer subject to
* the constraints
* @return new value along direction p from xold, null if no step was taken
* @throws Exception if an error occurs
*/
public double[] lnsrch(double[] xold, double[] gradient,
double[] direct, double stpmax,
boolean[] isFixed, double[][] nwsBounds,
DynamicIntArray wsBdsIndx)
throws Exception {
int i, k,len=xold.length,
fixedOne=-1; // idx of variable to be fixed
double alam, alamin; // lambda to be found, and its lower bound
// For convergence and bound test
double temp,test,alpha=Double.POSITIVE_INFINITY,fold=m_f,sum;
// For cubic interpolation
double a,alam2=0,b,disc=0,maxalam=1.0,rhs1,rhs2,tmplam;
double[] x = new double[len]; // New variable values
// Scale the step
for (sum=0.0,i=0;i<len;i++){
if(!isFixed[i]) // For fixed variables, direction = 0
sum += direct[i]*direct[i];
}
sum = Math.sqrt(sum);
if (m_Debug)
System.err.println("fold: "+Utils.doubleToString(fold,10,7)+"\n"+
"sum: "+Utils.doubleToString(sum,10,7)+"\n"+
"stpmax: "+Utils.doubleToString(stpmax,10,7));
if (sum > stpmax){
for (i=0;i<len;i++)
if(!isFixed[i])
direct[i] *= stpmax/sum;
}
else
maxalam = stpmax/sum;
// Compute initial rate of decrease, g'*d
m_Slope=0.0;
for (i=0;i<len;i++){
x[i] = xold[i];
if(!isFixed[i])
m_Slope += gradient[i]*direct[i];
}
if (m_Debug)
System.err.print("slope: " + Utils.doubleToString(m_Slope,10,7)+ "\n");
// Slope too small
if(Math.abs(m_Slope)<=m_Zero){
if (m_Debug)
System.err.println("Gradient and direction orthogonal -- "+
"Min. found with current fixed variables"+
" (or all variables fixed). Try to release"+
" some variables now.");
return x;
}
// Err: slope > 0
if(m_Slope > m_Zero){
if(m_Debug)
for(int h=0; h<x.length; h++)
System.err.println(h+": isFixed="+isFixed[h]+", x="+
x[h]+", grad="+gradient[h]+", direct="+
direct[h]);
throw new Exception("g'*p positive! -- Try to debug from here: line 327.");
}
// Compute LAMBDAmin and upper bound of lambda--alpha
test=0.0;
for(i=0;i<len;i++){
if(!isFixed[i]){// No need for fixed variables
temp=Math.abs(direct[i])/Math.max(Math.abs(x[i]),1.0);
if (temp > test) test=temp;
}
}
if(test>m_Zero) // Not converge
alamin = m_TOLX/test;
else{
if (m_Debug)
System.err.println("Zero directions for all free variables -- "+
"Min. found with current fixed variables"+
" (or all variables fixed). Try to release"+
" some variables now.");
return x;
}
// Check whether any non-working-set bounds are "binding"
for(i=0;i<len;i++){
if(!isFixed[i]){// No need for fixed variables
double alpi;
if((direct[i]<-m_Epsilon) && !Double.isNaN(nwsBounds[0][i])){//Not feasible
alpi = (nwsBounds[0][i]-xold[i])/direct[i];
if(alpi <= m_Zero){ // Zero
if (m_Debug)
System.err.println("Fix variable "+i+
" to lower bound "+ nwsBounds[0][i]+
" from value "+ xold[i]);
x[i] = nwsBounds[0][i];
isFixed[i]=true; // Fix this variable
alpha = 0.0;
nwsBounds[0][i]=Double.NaN; //Add cons. to working set
wsBdsIndx.addElement(i);
}
else if(alpha > alpi){ // Fix one variable in one iteration
alpha = alpi;
fixedOne = i;
}
}
else if((direct[i]>m_Epsilon) && !Double.isNaN(nwsBounds[1][i])){//Not feasible
alpi = (nwsBounds[1][i]-xold[i])/direct[i];
if(alpi <= m_Zero){ // Zero
if (m_Debug)
System.err.println("Fix variable "+i+
" to upper bound "+ nwsBounds[1][i]+
" from value "+ xold[i]);
x[i] = nwsBounds[1][i];
isFixed[i]=true; // Fix this variable
alpha = 0.0;
nwsBounds[1][i]=Double.NaN; //Add cons. to working set
wsBdsIndx.addElement(i);
}
else if(alpha > alpi){
alpha = alpi;
fixedOne = i;
}
}
}
}
if (m_Debug){
System.err.println("alamin: " + Utils.doubleToString(alamin,10,7));
System.err.println("alpha: " + Utils.doubleToString(alpha,10,7));
}
if(alpha <= m_Zero){ // Zero
m_IsZeroStep = true;
if (m_Debug)
System.err.println("Alpha too small, try again");
return x;
}
alam = alpha; // Always try full feasible newton step
if(alam > 1.0)
alam = 1.0;
// Iteration of one newton step, if necessary, backtracking is done
double initF=fold, // Initial function value
hi=alam, lo=alam, newSlope=0, fhi=m_f, flo=m_f;// Variables used for beta condition
double[] newGrad; // Gradient on the new variable values
kloop:
for (k=0;;k++) {
if(m_Debug)
System.err.println("\nLine search iteration: " + k);
for (i=0;i<len;i++){
if(!isFixed[i]){
x[i] = xold[i]+alam*direct[i]; // Compute xnew
if(!Double.isNaN(nwsBounds[0][i]) && (x[i]<nwsBounds[0][i])){
x[i] = nwsBounds[0][i]; //Rounding error
}
else if(!Double.isNaN(nwsBounds[1][i]) && (x[i]>nwsBounds[1][i])){
x[i] = nwsBounds[1][i]; //Rounding error
}
}
}
m_f = objectiveFunction(x); // Compute fnew
if(Double.isNaN(m_f))
throw new Exception("Objective function value is NaN!");
while(Double.isInfinite(m_f)){ // Avoid infinity
if(m_Debug)
System.err.println("Too large m_f. Shrink step by half.");
alam *= 0.5; // Shrink by half
if(alam <= m_Epsilon){
if(m_Debug)
System.err.println("Wrong starting points, change them!");
return x;
}
for (i=0;i<len;i++)
if(!isFixed[i])
x[i] = xold[i]+alam*direct[i];
m_f = objectiveFunction(x);
if(Double.isNaN(m_f))
throw new Exception("Objective function value is NaN!");
initF = Double.POSITIVE_INFINITY;
}
if(m_Debug) {
System.err.println("obj. function: " +
Utils.doubleToString(m_f, 10, 7));
System.err.println("threshold: " +
Utils.doubleToString(fold+m_ALF*alam*m_Slope,10,7));
}
if(m_f<=fold+m_ALF*alam*m_Slope){// Alpha condition: sufficient function decrease
if(m_Debug)
System.err.println("Sufficient function decrease (alpha condition): ");
newGrad = evaluateGradient(x);
for(newSlope=0.0,i=0; i<len; i++)
if(!isFixed[i])
newSlope += newGrad[i]*direct[i];
if (m_Debug)
System.err.println("newSlope: " + newSlope);
if(newSlope >= m_BETA*m_Slope){ // Beta condition: ensure pos. defnty.
if(m_Debug)
System.err.println("Increasing derivatives (beta condition): ");
if((fixedOne!=-1) && (alam>=alpha)){ // Has bounds and over
if(direct[fixedOne] > 0){
x[fixedOne] = nwsBounds[1][fixedOne]; // Avoid rounding error
nwsBounds[1][fixedOne]=Double.NaN; //Add cons. to working set
}
else{
x[fixedOne] = nwsBounds[0][fixedOne]; // Avoid rounding error
nwsBounds[0][fixedOne]=Double.NaN; //Add cons. to working set
}
if(m_Debug)
System.err.println("Fix variable "
+fixedOne+" to bound "+ x[fixedOne]+
" from value "+ xold[fixedOne]);
isFixed[fixedOne]=true; // Fix the variable
wsBdsIndx.addElement(fixedOne);
}
return x;
}
else if(k==0){ // First time: increase alam
// Search for the smallest value not complying with alpha condition
double upper = Math.min(alpha,maxalam);
if(m_Debug)
System.err.println("Alpha condition holds, increase alpha... ");
while(!((alam>=upper) || (m_f>fold+m_ALF*alam*m_Slope))){
lo = alam;
flo = m_f;
alam *= 2.0;
if(alam>=upper) // Avoid rounding errors
alam=upper;
for (i=0;i<len;i++)
if(!isFixed[i])
x[i] = xold[i]+alam*direct[i];
m_f = objectiveFunction(x);
if(Double.isNaN(m_f))
throw new Exception("Objective function value is NaN!");
newGrad = evaluateGradient(x);
for(newSlope=0.0,i=0; i<len; i++)
if(!isFixed[i])
newSlope += newGrad[i]*direct[i];
if(newSlope >= m_BETA*m_Slope){
if (m_Debug)
System.err.println("Increasing derivatives (beta condition): \n"+
"newSlope = "+Utils.doubleToString(newSlope,10,7));
if((fixedOne!=-1) && (alam>=alpha)){ // Has bounds and over
if(direct[fixedOne] > 0){
x[fixedOne] = nwsBounds[1][fixedOne]; // Avoid rounding error
nwsBounds[1][fixedOne]=Double.NaN; //Add cons. to working set
}
else{
x[fixedOne] = nwsBounds[0][fixedOne]; // Avoid rounding error
nwsBounds[0][fixedOne]=Double.NaN; //Add cons. to working set
}
if(m_Debug)
System.err.println("Fix variable "
+fixedOne+" to bound "+ x[fixedOne]+
" from value "+ xold[fixedOne]);
isFixed[fixedOne]=true; // Fix the variable
wsBdsIndx.addElement(fixedOne);
}
return x;
}
}
hi = alam;
fhi = m_f;
break kloop;
}
else{
if(m_Debug)
System.err.println("Alpha condition holds.");
hi = alam2; lo = alam; flo = m_f;
break kloop;
}
}
else if (alam < alamin) { // No feasible lambda found
if(initF<fold){
alam = Math.min(1.0,alpha);
for (i=0;i<len;i++)
if(!isFixed[i])
x[i] = xold[i]+alam*direct[i]; //Still take Alpha
if (m_Debug)
System.err.println("No feasible lambda: still take"+
" alpha="+alam);
if((fixedOne!=-1) && (alam>=alpha)){ // Has bounds and over
if(direct[fixedOne] > 0){
x[fixedOne] = nwsBounds[1][fixedOne]; // Avoid rounding error
nwsBounds[1][fixedOne]=Double.NaN; //Add cons. to working set
}
else{
x[fixedOne] = nwsBounds[0][fixedOne]; // Avoid rounding error
nwsBounds[0][fixedOne]=Double.NaN; //Add cons. to working set
}
if(m_Debug)
System.err.println("Fix variable "
+fixedOne+" to bound "+ x[fixedOne]+
" from value "+ xold[fixedOne]);
isFixed[fixedOne]=true; // Fix the variable
wsBdsIndx.addElement(fixedOne);
}
}
else{ // Convergence on delta(x)
for(i=0;i<len;i++)
x[i]=xold[i];
m_f=fold;
if (m_Debug)
System.err.println("Cannot find feasible lambda");
}
return x;
}
else { // Backtracking by polynomial interpolation
if(k==0){ // First time backtrack: quadratic interpolation
if(!Double.isInfinite(initF))
initF = m_f;
// lambda = -g'(0)/(2*g''(0))
tmplam = -0.5*alam*m_Slope/((m_f-fold)/alam-m_Slope);
}
else { // Subsequent backtrack: cubic interpolation
rhs1 = m_f-fold-alam*m_Slope;
rhs2 = fhi-fold-alam2*m_Slope;
a=(rhs1/(alam*alam)-rhs2/(alam2*alam2))/(alam-alam2);
b=(-alam2*rhs1/(alam*alam)+alam*rhs2/(alam2*alam2))/(alam-alam2);
if (a == 0.0) tmplam = -m_Slope/(2.0*b);
else {
disc=b*b-3.0*a*m_Slope;
if (disc < 0.0) disc = 0.0;
double numerator = -b+Math.sqrt(disc);
if(numerator >= Double.MAX_VALUE){
numerator = Double.MAX_VALUE;
if (m_Debug)
System.err.print("-b+sqrt(disc) too large! Set it to MAX_VALUE.");
}
tmplam=numerator/(3.0*a);
}
if (m_Debug)
System.err.print("Cubic interpolation: \n" +
"a: " + Utils.doubleToString(a,10,7)+ "\n" +
"b: " + Utils.doubleToString(b,10,7)+ "\n" +
"disc: " + Utils.doubleToString(disc,10,7)+ "\n" +
"tmplam: " + tmplam + "\n" +
"alam: " + Utils.doubleToString(alam,10,7)+ "\n");
if (tmplam>0.5*alam)
tmplam=0.5*alam; // lambda <= 0.5*lambda_old
}
}
alam2=alam;
fhi=m_f;
alam=Math.max(tmplam,0.1*alam); // lambda >= 0.1*lambda_old
if(alam>alpha){
throw new Exception("Sth. wrong in lnsrch:"+
"Lambda infeasible!(lambda="+alam+
", alpha="+alpha+", upper="+tmplam+
"|"+(-alpha*m_Slope/(2.0*((m_f-fold)/alpha-m_Slope)))+
", m_f="+m_f+", fold="+fold+
", slope="+m_Slope);
}
} // Endfor(k=0;;k++)
// Quadratic interpolation between lamda values between lo and hi.
// If cannot find a value satisfying beta condition, use lo.
double ldiff = hi-lo, lincr;
if(m_Debug)
System.err.println("Last stage of searching for beta condition (alam between "
+Utils.doubleToString(lo,10,7)+" and "
+Utils.doubleToString(hi,10,7)+")...\n"+
"Quadratic Interpolation(QI):\n"+
"Last newSlope = "+Utils.doubleToString(newSlope, 10, 7));
while((newSlope<m_BETA*m_Slope) && (ldiff>=alamin)){
lincr = -0.5*newSlope*ldiff*ldiff/(fhi-flo-newSlope*ldiff);
if(m_Debug)
System.err.println("fhi = "+fhi+"\n"+
"flo = "+flo+"\n"+
"ldiff = "+ldiff+"\n"+
"lincr (using QI) = "+lincr+"\n");
if(lincr<0.2*ldiff) lincr=0.2*ldiff;
alam = lo+lincr;
if(alam >= hi){ // We cannot go beyond the bounds, so the best we can try is hi
alam=hi;
lincr=ldiff;
}
for (i=0;i<len;i++)
if(!isFixed[i])
x[i] = xold[i]+alam*direct[i];
m_f = objectiveFunction(x);
if(Double.isNaN(m_f))
throw new Exception("Objective function value is NaN!");
if(m_f>fold+m_ALF*alam*m_Slope){
// Alpha condition fails, shrink lambda_upper
ldiff = lincr;
fhi = m_f;
}
else{ // Alpha condition holds
newGrad = evaluateGradient(x);
for(newSlope=0.0,i=0; i<len; i++)
if(!isFixed[i])
newSlope += newGrad[i]*direct[i];
if(newSlope < m_BETA*m_Slope){
// Beta condition fails, shrink lambda_lower
lo = alam;
ldiff -= lincr;
flo = m_f;
}
}
}
if(newSlope < m_BETA*m_Slope){ // Cannot satisfy beta condition, take lo
if(m_Debug)
System.err.println("Beta condition cannot be satisfied, take alpha condition");
alam=lo;
for (i=0;i<len;i++)
if(!isFixed[i])
x[i] = xold[i]+alam*direct[i];
m_f = flo;
}
else if(m_Debug)
System.err.println("Both alpha and beta conditions are satisfied. alam="
+Utils.doubleToString(alam,10,7));
if((fixedOne!=-1) && (alam>=alpha)){ // Has bounds and over
if(direct[fixedOne] > 0){
x[fixedOne] = nwsBounds[1][fixedOne]; // Avoid rounding error
nwsBounds[1][fixedOne]=Double.NaN; //Add cons. to working set
}
else{
x[fixedOne] = nwsBounds[0][fixedOne]; // Avoid rounding error
nwsBounds[0][fixedOne]=Double.NaN; //Add cons. to working set
}
if(m_Debug)
System.err.println("Fix variable "
+fixedOne+" to bound "+ x[fixedOne]+
" from value "+ xold[fixedOne]);
isFixed[fixedOne]=true; // Fix the variable
wsBdsIndx.addElement(fixedOne);
}
return x;
}
/**
* Main algorithm. Descriptions see "Practical Optimization"
*
* @param initX initial point of x, assuming no value's on the bound!
* @param constraints the bound constraints of each variable
* constraints[0] is the lower bounds and
* constraints[1] is the upper bounds
* @return the solution of x, null if number of iterations not enough
* @throws Exception if an error occurs
*/
public double[] findArgmin(double[] initX, double[][] constraints)
throws Exception{
int l = initX.length;
// Initially all variables are free, all bounds are constraints of
// non-working-set constraints
boolean[] isFixed = new boolean[l];
double[][] nwsBounds = new double[2][l];
// Record indice of fixed variables, simply for efficiency
DynamicIntArray wsBdsIndx = new DynamicIntArray(constraints.length);
// Vectors used to record the variable indices to be freed
DynamicIntArray toFree=null, oldToFree=null;
// Initial value of obj. function, gradient and inverse of the Hessian
m_f = objectiveFunction(initX);
if(Double.isNaN(m_f))
throw new Exception("Objective function value is NaN!");
double sum=0;
double[] grad=evaluateGradient(initX), oldGrad, oldX,
deltaGrad=new double[l], deltaX=new double[l],
direct = new double[l], x = new double[l];
Matrix L = new Matrix(l, l); // Lower triangle of Cholesky factor
double[] D = new double[l]; // Diagonal of Cholesky factor
for(int i=0; i<l; i++){
// L.setRow(i, new double[l]); Not necessary
L.set(i,i,1.0);
D[i] = 1.0;
direct[i] = -grad[i];
sum += grad[i]*grad[i];
x[i] = initX[i];
nwsBounds[0][i] = constraints[0][i];
nwsBounds[1][i] = constraints[1][i];
isFixed[i] = false;
}
double stpmax = m_STPMX*Math.max(Math.sqrt(sum), l);
iterates:
for(int step=0; step < m_MAXITS; step++){
if (m_Debug)
System.err.println("\nIteration # " + step + ":");
// Try at most one feasible newton step, i.e. 0<lamda<=alpha
oldX = x;
oldGrad = grad;
// Also update grad
if (m_Debug)
System.err.println("Line search ... ");
m_IsZeroStep = false;
x=lnsrch(x, grad, direct, stpmax,
isFixed, nwsBounds, wsBdsIndx);
if (m_Debug)
System.err.println("Line search finished.");
if(m_IsZeroStep){ // Zero step, simply delete rows/cols of D and L
for(int f=0; f<wsBdsIndx.size(); f++){
int[] idx = new int[1];
// int idx=wsBdsIndx.elementAt(f);
idx[0] = wsBdsIndx.elementAt(f);
L.setMatrix(idx, 0, l - 1, new Matrix(1, l));
// L.setRow(idx, new double[l]);
L.setMatrix(0, l - 1, idx, new Matrix(l, 1));
// L.setColumn(idx, new double[l]);
D[idx[0]] = 0.0;
// D[idx] = 0.0;
}
grad = evaluateGradient(x);
step--;
}
else{
// Check converge on x
boolean finish = false;
double test=0.0;
for(int h=0; h<l; h++){
deltaX[h] = x[h]-oldX[h];
double tmp=Math.abs(deltaX[h])/
Math.max(Math.abs(x[h]), 1.0);
if(tmp > test) test = tmp;
}
if(test < m_Zero){
if (m_Debug)
System.err.println("\nDeltaX converge: "+test);
finish = true;
}
// Check zero gradient
grad = evaluateGradient(x);
test=0.0;
double denom=0.0, dxSq=0.0, dgSq=0.0, newlyBounded=0.0;
for(int g=0; g<l; g++){
if(!isFixed[g]){
deltaGrad[g] = grad[g] - oldGrad[g];
// Calculate the denominators
denom += deltaX[g]*deltaGrad[g];
dxSq += deltaX[g]*deltaX[g];
dgSq += deltaGrad[g]*deltaGrad[g];
}
else // Only newly bounded variables will be non-zero
newlyBounded += deltaX[g]*(grad[g]-oldGrad[g]);
// Note: CANNOT use projected gradient for testing
// convergence because of newly bounded variables
double tmp = Math.abs(grad[g])*
Math.max(Math.abs(direct[g]),1.0)/
Math.max(Math.abs(m_f),1.0);
if(tmp > test) test = tmp;
}
if(test < m_Zero){
if (m_Debug)
System.err.println("Gradient converge: "+test);
finish = true;
}
// dg'*dx could be < 0 using inexact lnsrch
if(m_Debug)
System.err.println("dg'*dx="+(denom+newlyBounded));
// dg'*dx = 0
if(Math.abs(denom+newlyBounded) < m_Zero)
finish = true;
int size = wsBdsIndx.size();
boolean isUpdate = true; // Whether to update BFGS formula
// Converge: check whether release any current constraints
if(finish){
if (m_Debug)
System.err.println("Test any release possible ...");
if(toFree != null)
oldToFree = (DynamicIntArray)toFree.copy();
toFree = new DynamicIntArray(wsBdsIndx.size());
for(int m=size-1; m>=0; m--){
int index=wsBdsIndx.elementAt(m);
double[] hessian = evaluateHessian(x, index);
double deltaL=0.0;
if(hessian != null){
for(int mm=0; mm<hessian.length; mm++)
if(!isFixed[mm]) // Free variable
deltaL += hessian[mm]*direct[mm];
}
// First and second order Lagrangian multiplier estimate
// If user didn't provide Hessian, use first-order only
double L1, L2;
if(x[index] >= constraints[1][index]) // Upper bound
L1 = -grad[index];
else if(x[index] <= constraints[0][index])// Lower bound
L1 = grad[index];
else
throw new Exception("x["+index+"] not fixed on the"+
" bounds where it should have been!");
// L2 = L1 + deltaL
L2 = L1 + deltaL;
if (m_Debug)
System.err.println("Variable "+index+
": Lagrangian="+L1+"|"+L2);
//Check validity of Lagrangian multiplier estimate
boolean isConverge =
(2.0*Math.abs(deltaL)) < Math.min(Math.abs(L1),
Math.abs(L2));
if((L1*L2>0.0) && isConverge){ //Same sign and converge: valid
if(L2 < 0.0){// Negative Lagrangian: feasible
toFree.addElement(index);
wsBdsIndx.removeElementAt(m);
finish=false; // Not optimal, cannot finish
}
}
// Although hardly happen, better check it
// If the first-order Lagrangian multiplier estimate is wrong,
// avoid zigzagging
if((hessian==null) && (toFree != null) && toFree.equal(oldToFree))
finish = true;
}
if(finish){// Min. found
if (m_Debug)
System.err.println("Minimum found.");
m_f = objectiveFunction(x);
if(Double.isNaN(m_f))
throw new Exception("Objective function value is NaN!");
return x;
}
// Free some variables
for(int mmm=0; mmm<toFree.size(); mmm++){
int freeIndx=toFree.elementAt(mmm);
isFixed[freeIndx] = false; // Free this variable
if(x[freeIndx] <= constraints[0][freeIndx]){// Lower bound
nwsBounds[0][freeIndx] = constraints[0][freeIndx];
if (m_Debug)
System.err.println("Free variable "+freeIndx+
" from bound "+
nwsBounds[0][freeIndx]);
}
else{ // Upper bound
nwsBounds[1][freeIndx] = constraints[1][freeIndx];
if (m_Debug)
System.err.println("Free variable "+freeIndx+
" from bound "+
nwsBounds[1][freeIndx]);
}
L.set(freeIndx, freeIndx, 1.0);
D[freeIndx] = 1.0;
isUpdate = false;
}
}
if(denom<Math.max(m_Zero*Math.sqrt(dxSq)*Math.sqrt(dgSq), m_Zero)){
if (m_Debug)
System.err.println("dg'*dx negative!");
isUpdate = false; // Do not update
}
// If Hessian will be positive definite, update it
if(isUpdate){
// modify once: dg*dg'/(dg'*dx)
double coeff = 1.0/denom; // 1/(dg'*dx)
updateCholeskyFactor(L,D,deltaGrad,coeff,isFixed);
// modify twice: g*g'/(g'*p)
coeff = 1.0/m_Slope; // 1/(g'*p)
updateCholeskyFactor(L,D,oldGrad,coeff,isFixed);
}
}
// Find new direction
Matrix LD = new Matrix(l,l); // L*D
double[] b = new double[l];
for(int k=0; k<l; k++){
if(!isFixed[k]) b[k] = -grad[k];
else b[k] = 0.0;
for(int j=k; j<l; j++){ // Lower triangle
if(!isFixed[j] && !isFixed[k])
LD.set(j, k, L.get(j,k)*D[k]);
}
}
// Solve (LD)*y = -g, where y=L'*direct
double[] LDIR = solveTriangle(LD, b, true, isFixed);
LD = null;
for(int m=0; m<LDIR.length; m++){
if(Double.isNaN(LDIR[m]))
throw new Exception("L*direct["+m+"] is NaN!"
+"|-g="+b[m]+"|"+isFixed[m]
+"|diag="+D[m]);
}
// Solve L'*direct = y
direct = solveTriangle(L, LDIR, false, isFixed);
for(int m=0; m<direct.length; m++){
if(Double.isNaN(direct[m]))
throw new Exception("direct is NaN!");
}
//System.gc();
}
if(m_Debug)
System.err.println("Cannot find minimum"+
" -- too many interations!");
m_X = x;
return null;
}
/**
* Solve the linear equation of TX=B where T is a triangle matrix
* It can be solved using back/forward substitution, with O(N^2)
* complexity
* @param t the matrix T
* @param b the vector B
* @param isLower whether T is a lower or higher triangle matrix
* @param isZero which row(s) of T are not used when solving the equation.
* If it's null or all 'false', then every row is used.
* @return the solution of X
*/
public static double[] solveTriangle(Matrix t, double[] b,
boolean isLower, boolean[] isZero){
int n = b.length;
double[] result = new double[n];
if(isZero == null)
isZero = new boolean[n];
if(isLower){ // lower triangle, forward-substitution
int j = 0;
while((j<n)&&isZero[j]){result[j]=0.0; j++;} // go to the first row
if(j<n){
result[j] = b[j]/t.get(j,j);
for(; j<n; j++){
if(!isZero[j]){
double numerator=b[j];
for(int k=0; k<j; k++)
numerator -= t.get(j,k)*result[k];
result[j] = numerator/t.get(j,j);
}
else
result[j] = 0.0;
}
}
}
else{ // Upper triangle, back-substitution
int j=n-1;
while((j>=0)&&isZero[j]){result[j]=0.0; j--;} // go to the last row
if(j>=0){
result[j] = b[j]/t.get(j,j);
for(; j>=0; j--){
if(!isZero[j]){
double numerator=b[j];
for(int k=j+1; k<n; k++)
numerator -= t.get(k,j)*result[k];
result[j] = numerator/t.get(j,j);
}
else
result[j] = 0.0;
}
}
}
return result;
}
/**
* One rank update of the Cholesky factorization of B matrix in BFGS updates,
* i.e. B = LDL', and B_{new} = LDL' + coeff*(vv') where L is a unit lower triangle
* matrix and D is a diagonal matrix, and v is a vector.<br/>
* When coeff > 0, we use C1 algorithm, and otherwise we use C2 algorithm described
* in ``Methods for Modifying Matrix Factorizations''
*
* @param L the unit triangle matrix L
* @param D the diagonal matrix D
* @param v the update vector v
* @param coeff the coeffcient of update
* @param isFixed which variables are not to be updated
*/
protected void updateCholeskyFactor(Matrix L, double[] D,
double[] v, double coeff,
boolean[] isFixed)
throws Exception{
double t, p, b;
int n = v.length;
double[] vp = new double[n];
for (int i=0; i<v.length; i++)
if(!isFixed[i])
vp[i]=v[i];
else
vp[i]=0.0;
if(coeff>0.0){
t = coeff;
for(int j=0; j<n; j++){
if(isFixed[j]) continue;
p = vp[j];
double d=D[j], dbarj=d+t*p*p;
D[j] = dbarj;
b = p*t/dbarj;
t *= d/dbarj;
for(int r=j+1; r<n; r++){
if(!isFixed[r]){
double l=L.get(r, j);
vp[r] -= p*l;
L.set(r, j, l+b*vp[r]);
}
else
L.set(r, j, 0.0);
}
}
}
else{
double[] P = solveTriangle(L, v, true, isFixed);
t = 0.0;
for(int i=0; i<n; i++)
if(!isFixed[i])
t += P[i]*P[i]/D[i];
double sqrt=1.0+coeff*t;
sqrt = (sqrt<0.0)? 0.0 : Math.sqrt(sqrt);
double alpha=coeff, sigma=coeff/(1.0+sqrt), rho, theta;
for(int j=0; j<n; j++){
if(isFixed[j]) continue;
double d=D[j];
p = P[j]*P[j]/d;
theta = 1.0+sigma*p;
t -= p;
if(t<0.0) t=0.0; // Rounding error
double plus = sigma*sigma*p*t;
if((j<n-1) && (plus <= m_Zero))
plus=m_Zero; // Avoid rounding error
rho = theta*theta + plus;
D[j] = rho*d;
if(Double.isNaN(D[j])){
throw new Exception("d["+j+"] NaN! P="+P[j]+",d="+d+
",t="+t+",p="+p+",sigma="+sigma+
",sclar="+coeff);
}
b=alpha*P[j]/(rho*d);
alpha /= rho;
rho = Math.sqrt(rho);
double sigmaOld = sigma;
sigma *= (1.0+rho)/(rho*(theta+rho));
if((j<n-1) &&
(Double.isNaN(sigma) || Double.isInfinite(sigma)))
throw new Exception("sigma NaN/Inf! rho="+rho+
",theta="+theta+",P["+j+"]="+
P[j]+",p="+p+",d="+d+",t="+t+
",oldsigma="+sigmaOld);
for(int r=j+1; r<n; r++){
if(!isFixed[r]){
double l=L.get(r, j);
vp[r] -= P[j]*l;
L.set(r, j, l+b*vp[r]);
}
else
L.set(r, j, 0.0);
}
}
}
}
/**
* Implements a simple dynamic array for ints.
*/
protected class DynamicIntArray
implements RevisionHandler {
/** The int array. */
private int[] m_Objects;
/** The current size; */
private int m_Size = 0;
/** The capacity increment */
private int m_CapacityIncrement = 1;
/** The capacity multiplier. */
private int m_CapacityMultiplier = 2;
/**
* Constructs a vector with the given capacity.
*
* @param capacity the vector's initial capacity
*/
public DynamicIntArray(int capacity) {
m_Objects = new int[capacity];
}
/**
* Adds an element to this vector. Increases its
* capacity if its not large enough.
*
* @param element the element to add
*/
public final void addElement(int element) {
if (m_Size == m_Objects.length) {
int[] newObjects;
newObjects = new int[m_CapacityMultiplier *
(m_Objects.length +
m_CapacityIncrement)];
System.arraycopy(m_Objects, 0, newObjects, 0, m_Size);
m_Objects = newObjects;
}
m_Objects[m_Size] = element;
m_Size++;
}
/**
* Produces a copy of this vector.
*
* @return the new vector
*/
public final Object copy() {
DynamicIntArray copy = new DynamicIntArray(m_Objects.length);
copy.m_Size = m_Size;
copy.m_CapacityIncrement = m_CapacityIncrement;
copy.m_CapacityMultiplier = m_CapacityMultiplier;
System.arraycopy(m_Objects, 0, copy.m_Objects, 0, m_Size);
return copy;
}
/**
* Returns the element at the given position.
*
* @param index the element's index
* @return the element with the given index
*/
public final int elementAt(int index) {
return m_Objects[index];
}
/**
* Check whether the two integer vectors equal to each other
* Two integer vectors are equal if all the elements are the
* same, regardless of the order of the elements
*
* @param b another integer vector
* @return whether they are equal
*/
private boolean equal(DynamicIntArray b){
if((b==null) || (size()!=b.size()))
return false;
int size=size();
// Only values matter, order does not matter
int[] sorta=Utils.sort(m_Objects), sortb=Utils.sort(b.m_Objects);
for(int j=0; j<size;j++)
if(m_Objects[sorta[j]] != b.m_Objects[sortb[j]])
return false;
return true;
}
/**
* Deletes an element from this vector.
*
* @param index the index of the element to be deleted
*/
public final void removeElementAt(int index) {
System.arraycopy(m_Objects, index + 1, m_Objects, index,
m_Size - index - 1);
m_Size--;
}
/**
* Removes all components from this vector and sets its
* size to zero.
*/
public final void removeAllElements() {
m_Objects = new int[m_Objects.length];
m_Size = 0;
}
/**
* Returns the vector's current size.
*
* @return the vector's current size
*/
public final int size() {
return m_Size;
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 8076 $");
}
}
}