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/*
* Modification History
*
* 2001-August-30 Jason Rohrer
* Created.
*
* 2001-August-31 Jason Rohrer
* Finished implementation.
* Fixed a compile bug.
*
* 2001-September-4 Jason Rohrer
* Added support for FixedConstantExpressions.
*/
#ifndef RANDOM_EXPRESSION_FACTORY_INCLUDED
#define RANDOM_EXPRESSION_FACTORY_INCLUDED
#include "Expression.h"
#include "ConstantExpression.h"
#include "FixedConstantExpression.h"
#include "InvertExpression.h"
#include "ProductExpression.h"
#include "PowerExpression.h"
#include "SumExpression.h"
#include "NegateExpression.h"
#include "SinExpression.h"
#include "minorGems/util/random/RandomSource.h"
/**
* Utility class for constructing random expressions.
*
* @author Jason Rohrer
*/
class RandomExpressionFactory {
public:
/**
* Constructs a random expression factory.
*
* @param inRandSource the source for random numbers
* to use while constructing expressions.
* Must be destroyed by caller after this class is destroyed.
*/
RandomExpressionFactory( RandomSource *inRandSource );
/**
* Recursively constructs a random expression with all parameters
* filled.
*
* @param inProbOfStopping the probability of stopping at each
* branch of the expression. Upon stopping on a certain branch
* of the recursion, it simply returns a constant expression.
* @param inProbOfFixedConstant the probability of a fixed
* constant expression being inserted upon stopping (as opposed
* to a (mutable) constant expression).
* @param inMaxDepth if this is reached, the recursion
* stops regardless of inProbOfStopping.
* @param inConstantMax the maximum value for a constant expression.
*
* @return the constructed expression.
*/
Expression *constructRandomExpression(
double inProbOfStopping, double inProbOfFixedConstant,
int inMaxDepth, double inConstantMax );
protected:
RandomSource *mRandSource;
};
inline RandomExpressionFactory::RandomExpressionFactory(
RandomSource *inRandSource )
: mRandSource( inRandSource ) {
}
inline Expression *RandomExpressionFactory::constructRandomExpression(
double inProbOfStopping,
double inProbOfFixedConstant,
int inMaxDepth, double inConstantMax ) {
// fill in constant expressions only at the leaves
if( inMaxDepth == 0 ||
mRandSource->getRandomDouble() <= inProbOfStopping ) {
// stop
if( mRandSource->getRandomDouble() <= inProbOfFixedConstant ) {
return new FixedConstantExpression(
inConstantMax * ( mRandSource->getRandomDouble() ) );
}
else {
return new ConstantExpression(
inConstantMax * ( mRandSource->getRandomDouble() ) );
}
}
else {
// keep filling in non constant expressions randomly
// FILL IN HERE
// we have 6 expression types
int randVal = mRandSource->getRandomBoundedInt( 0, 3 );
Expression *outExpression;
// pick an expression type
switch( randVal ) {
case 0:
outExpression = new NegateExpression( NULL );
break;
case 1:
outExpression = new ProductExpression( NULL, NULL );
break;
case 2:
outExpression = new SinExpression( NULL );
break;
case 3:
outExpression = new SumExpression( NULL, NULL );
break;
default:
// should never happen, but...
printf( "RandomExpressionFactory: " );
printf( "Error while generating random expression\n" );
// default to a constant expression of 0
outExpression = new ConstantExpression( 0 );
break;
}
// now recursively fill in the arguments in succession
for( int i=0; i<outExpression->getNumArguments(); i++ ) {
// create a random expression as the argument
// note that we decrement inMaxDepth here
Expression *argument = constructRandomExpression(
inProbOfStopping, inProbOfFixedConstant,
inMaxDepth - 1, inConstantMax );
// set the argument into our expression
outExpression->setArgument( i, argument );
}
// now expression is complete.
return outExpression;
} // end of non-constant else case
} // end of constructRandomExpression()
#endif
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