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LinearMapper1d.hh
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#ifndef NPSTAT_LINEARMAPPER1D_HH_
#define NPSTAT_LINEARMAPPER1D_HH_
/*!
// \file LinearMapper1d.hh
//
// \brief Linear transformation functor
//
// Author: I. Volobouev
//
// October 2009
*/
#include <stdexcept>
namespace npstat {
/** Functor which performs linear mapping in 1-d */
class LinearMapper1d
{
public:
/** Default constructor builds an identity transformation */
inline LinearMapper1d() : a_(1.0), b_(0.0) {}
/**
// Transform definition from two points. The point at x0
// is mapped into y0, the point at x1 is mapped into y1.
// The linear transformation is thus fully defined.
*/
inline LinearMapper1d(const double x0, const double y0,
const double x1, const double y1)
{
const double dx = x1 - x0;
if (!dx) throw std::invalid_argument(
"In npstat::LinearMapper1d constructor: "
"invalid arguments (x0 == x1)");
a_ = (y1 - y0)/dx;
b_ = ((y0 + y1) - a_*(x0 + x1))/2.0;
}
/** Explicitly provide the transform coefficients as in y = ca*x + cb */
inline LinearMapper1d(const double ca, const double cb)
: a_(ca), b_(cb) {}
/** Perform the transformation */
inline double operator()(const double& x) const {return a_*x + b_;}
/** Get the linear coefficient of the transform */
inline double a() const {return a_;}
/** Get the transform constant */
inline double b() const {return b_;}
/** Create the inverse transform */
inline LinearMapper1d inverse() const
{
if (!a_) throw std::invalid_argument(
"In npstat::LinearMapper1d::inverse: "
"mapping is not invertible");
return LinearMapper1d(1.0/a_, -b_/a_);
}
/** Sequence of two transforms: the one on the right is applied first */
inline LinearMapper1d operator*(const LinearMapper1d& r) const
{
return LinearMapper1d(a_*r.a_, a_*r.b_ + b_);
}
private:
double a_;
double b_;
};
}
#endif // NPSTAT_LINEARMAPPER1D_HH_

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