base/VariableExpression

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/* **-*-c++-*-**************************************************************
  Copyright (C)2002 David Jung <opensim@pobox.com>

  This program/file 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 2 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. (http://www.gnu.org)
  
  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  
  $Id: VariableExpression 1029 2004-02-11 20:45:54Z jungd $
  $Revision: 1.12 $
  $Date: 2004-02-11 15:45:54 -0500 (Wed, 11 Feb 2004) $
  $Author: jungd $
 
****************************************************************************/

#ifndef _BASE_VARIABLEEXPRESSION_
#define _BASE_VARIABLEEXPRESSION_

#include <base/base>
#include <base/ConstantExpression>


namespace base {


//
// Expression that evaluates to a specific parameter variable from the params Vector
//

class VariableExpression : public ExpressionNode
{
public:
  VariableExpression(Int paramsIndex)
    : index(paramsIndex) {}
  VariableExpression(const VariableExpression& e)
    : index(e.index) {}

  virtual NodeType type() const { return NodeType(Leaf|Variable); } 

  virtual Object& clone() const { return *NewObj VariableExpression(*this); }
  virtual String className() const { return String("VariableExpression"); }

  virtual String toString() const { return String("p[")+base::intToString(index)+"]"; }

  virtual void serialize(Serializer& s) { s(index,"index"); }

protected:
  VariableExpression() {}
  
  virtual void cacheValue(const Vector& params) const
    { 
      if (index >= params.size())
        throw std::invalid_argument(Exception(String("Expression refers to variable index not present in evaluation parameter vector:")+base::intToString(index)));
      value = params[index]; valueCached=true; 
    }
  virtual void resetCache() const { valueCached=false; }

  virtual void cacheDerivative(Int withRespectToIndex) const 
    {
      derivative = ref<ExpressionNode>(NewObj ConstantExpression(( index==withRespectToIndex)?1:0 ));
      derivWithRespToIndex = withRespectToIndex;
      derivCached = true;
    }
  virtual void resetDerivCached() const { derivCached=false; derivative = ref<ExpressionNode>(0); }

  virtual void operationCounts(Int& addsub, Int& multdiv, Int& trig) const 
    {}

  Int index;

  friend class Expression;
  friend class Serializable::SerializableDerivedInstantiator<VariableExpression>;
};

} // base

#endif

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