til_math.h

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#ifndef TIL_MATH_H
#define TIL_MATH_H

// include from TIL library
#include "til/til_common.h"

namespace til {

        namespace math {


                INLINE double sinc(double x)
                {
                        const double EPSILON = 128 * std::numeric_limits<double>::epsilon();
                        // If x is too small, return assymptotic value
                        if (fabs(x) <= EPSILON) return 1.0;
                        // formula
                        return sin(x) / x;
                }


                INLINE double dsinc(double x)
                {
                        const double EPSILON = 128 * std::numeric_limits<double>::epsilon();
                        // If x is too small, return assymptotic value
                        if (fabs(x) <= EPSILON) return 0.0;
                        // formula
                        return cos(x) / x - sin(x) / (x*x);
                }

                INLINE double d2sinc(double x)
                {
                        const double EPSILON = 128 * std::numeric_limits<double>::epsilon();
                        // if x is too small, return assymptotic value
                        if (fabs(x) <= EPSILON) return -1.0 / 3.0;      
                        // formula
                        return 2*sin(x)/(x*x*x) - 2*cos(x)/(x*x) - sin(x)/x;
                }

        } // namespace math
} // namespace til

#endif