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[Math] Add custom derivative for digamma function #21401

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[Math] Add custom derivative for digamma function #21401

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5f97606
[Math] Add custom derivative for `digamma` function
guitargeek Feb 27, 2026
cdd7d17
[Math] Remove unneeded code from CladDerivator.h
guitargeek Feb 27, 2026
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31 changes: 9 additions & 22 deletions math/mathcore/inc/Math/CladDerivator.h
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Original file line number Diff line number Diff line change
Expand Up @@ -34,8 +34,7 @@

#include <stdexcept>

namespace clad {
namespace custom_derivatives {
namespace clad::custom_derivatives {
namespace TMath {
template <typename T>
ValueAndPushforward<T, T> Abs_pushforward(T x, T d_x)
Expand Down Expand Up @@ -206,24 +205,9 @@ ValueAndPushforward<T, T> TanH_pushforward(T x, T d_x)
return {::TMath::TanH(x), (1. / ::TMath::Sq(::TMath::CosH(x))) * d_x};
}

#ifdef WIN32
// Additional custom derivatives that can be removed
// after Issue #12108 in ROOT is resolved
// constexpr is removed
ValueAndPushforward<Double_t, Double_t> Pi_pushforward()
{
return {3.1415926535897931, 0.};
}
// constexpr is removed
ValueAndPushforward<Double_t, Double_t> Ln10_pushforward()
{
return {2.3025850929940459, 0.};
}
#endif
} // namespace TMath

namespace ROOT {
namespace Math {
namespace ROOT::Math {

inline void landau_pdf_pullback(double x, double xi, double x0, double d_out, double *d_x, double *d_xi, double *d_x0)
{
Expand Down Expand Up @@ -1092,13 +1076,16 @@ inline void inc_gamma_c_pullback(double a, double x, double _d_y, double *_d_a,
}
}

inline ValueAndPushforward<double, double> digamma_pushforward(double x, double d_x)
{
return {::ROOT::Math::digamma(x), ::ROOT::Math::trigamma(x) * d_x};
}

#endif // R__HAS_MATHMORE

} // namespace Math
} // namespace ROOT
} // namespace ROOT::Math

} // namespace custom_derivatives
} // namespace clad
} // namespace clad::custom_derivatives

// Forward declare BLAS functions.
extern "C" void sgemm_(const char *transa, const char *transb, const int *m, const int *n, const int *k,
Expand Down
1 change: 1 addition & 0 deletions math/mathmore/inc/Math/SpecFuncMathMore.h
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Expand Up @@ -874,6 +874,7 @@ namespace Math {
double wigner_9j(int two_ja, int two_jb, int two_jc, int two_jd, int two_je, int two_jf, int two_jg, int two_jh, int two_ji);

double digamma(double x);
double trigamma(double x);


} // namespace Math
Expand Down
5 changes: 5 additions & 0 deletions math/mathmore/src/SpecFuncMathMore.cxx
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Expand Up @@ -482,5 +482,10 @@ double digamma(double x)
return gsl_sf_psi(x);
}

double trigamma(double x)
{
return gsl_sf_psi_1(x);
}

} // namespace Math
} // namespace ROOT
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