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#ifndef __RVL_TOOLS_POLYOP_H_
#define __RVL_TOOLS_POLYOP_H_

#include "functions.hh"
#include "op.hh"

namespace RVL {

  /** This operator takes a vector of coefficients and computes the polynomial
      mapping described by these coefficients.  The coefficients are
      in ascending order of power (\f$ coef[0] + coef[1]*x + coef[2]*x^2 + \ldots\f$.
      Powers are computed elementwise, and the Vector::linComb method is used for
      addition and scaling.
  */
  template<class Scalar>
  class PolynomialOperator : public OperatorWithInvertibleDeriv<Scalar> {

  protected:
    Space<Scalar> & spc;
    std::valarray<Scalar> coef;

    /** 1-jet at a point, accessible only through OperatorEvaluation
	and subclasses.
    */
  
    /** \f$y = F(x)\f$ */
    virtual void apply(const Vector<Scalar> & x, 
		       Vector<Scalar> & y) const {
      Vector<Scalar> temp(x);
      ElementwiseMultiply<Scalar> dotstar;
      int size = coef.size();
      if( size > 0) {
	RVLAssignConst<Scalar> constantterm(coef[0]);
	y.eval(constantterm);
      }
      if( size > 1 )
	y.linComb(coef[1], temp);
      for( int i = 2; i < size; i++) {
	temp.eval(dotstar, temp, x);
	y.linComb(coef[i], temp);
      }
    }
  
    /** \f$dy = DF(x)dx\f$ */
    virtual void applyDeriv(const Vector<Scalar> & x, 
			    const Vector<Scalar> & dx,
			    Vector<Scalar> & dy) const {
      Vector<Scalar> temp(x);
      ElementwiseMultiply<Scalar> dotstar;
      int size = coef.size();
      if( size > 1) {
	RVLAssignConst<Scalar> constantterm(coef[1]);
	dy.eval(constantterm);
      } else {
	dy.zero();
      }  
      if( size > 2 )
	dy.linComb(coef[2]*Scalar(2), temp);
      for( int i = 3; i < size; i++) {
	temp.eval(dotstar, temp, x);
	dy.linComb(coef[i]*Scalar(i), temp);
      } 
      // dy has DF(x), so we need to do the multiply now.
      dy.eval(dotstar, dy,dx);
    }
  
    /** \f$dx = DF(x)^*dy\f$ */
    virtual void applyAdjDeriv(const Vector<Scalar> & x, 
			       const Vector<Scalar> & dy,
			       Vector<Scalar> & dx) const {
      applyDeriv(x,dy,dx);
    }

    /** Since this is a diagonal operator, the inverse of the derivative
	amounts to performing elementwise division.
    */
    void applyInverseDeriv(const Vector<Scalar> & x,
			   const Vector<Scalar> & dy,
			   Vector<Scalar> & dx) const {
      Vector<Scalar> temp(x);
      ElementwiseMultiply<Scalar> dotstar;
      int size = coef.size();
      if( size > 1) {
	RVLAssignConst<Scalar> constantterm(coef[1]);
	dx.eval(constantterm);
      } else {
	dx.zero();
      }  
      if( size > 2 )
	dx.linComb(coef[2]*Scalar(2), temp);
      for( int i = 3; i < size; i++) {
	temp.eval(dotstar, temp, x);
	dx.linComb(coef[i]*Scalar(i), temp);
      } 
      // dy has DF(x), so we need to do the division now.
      ElementwiseDivision<Scalar> dotslash;
      dx.eval(dotslash, dy, dx);
    }

    /** Diagonal op => symetric */
    void applyAdjInverseDeriv(const Vector<Scalar> & x,
			      const Vector<Scalar> & dx,
			      Vector<Scalar> & dy) const {
      applyInverseDeriv(x,dx,dy);
    }


    /** virtual copy contructor, also accessible only through
	OperatorEvaluation. Usually implemented with operator new and
	copy constructor of concrete child class. */
  
    virtual Operator<Scalar> * clone() const { return new PolynomialOperator(*this); }

  public:
  
    PolynomialOperator(const std::valarray<Scalar> & _coef, Space<Scalar> & _spc)
      : spc(_spc), coef(_coef) {}
    PolynomialOperator(const PolynomialOperator<Scalar> & s): spc(s.spc), coef(s.coef) {}
    ~PolynomialOperator() {}
  
    /** access to domain, range */
    virtual const Space<Scalar> & getDomain() const { return spc; }
    virtual const Space<Scalar> & getRange() const { return spc; }

    virtual void write(RVLException & e) const { 
      e << "PolynomialOperator with coefficients";
      for(int i = 0; i < coef.size(); i++) {
	e << "c[" << i << "] = " << coef[i] << '\n';
      }
    }

    virtual ostream & write(ostream & str) const { 
      str << "PolynomialOperator with coefficients";
      for(int i = 0; i < coef.size(); i++) {
	str << "c[" << i << "] = " << coef[i] << '\n';
      }
    }

  
  };


}

#endif