[Math] Add custom derivative for digamma function#21401
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guitargeek wants to merge 2 commits intoroot-project:masterfrom
Open
[Math] Add custom derivative for digamma function#21401guitargeek wants to merge 2 commits intoroot-project:masterfrom
digamma function#21401guitargeek wants to merge 2 commits intoroot-project:masterfrom
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The `digamma` function is important because it's the derivative of the log of the gamma function, which is widely used in likelihood fits because it appears in the Poisson distribution. If we want analytical Hessians, we also need to provide the analytical derivative of the digamma function, which is the trigamma function. Fortunately, we can find it in the GNU scientific library: https://www.gnu.org/software/gsl/doc/html/specfunc.html#trigamma-function
Test Results 22 files 22 suites 3d 3h 36m 14s ⏱️ For more details on these failures, see this check. Results for commit cdd7d17. |
vgvassilev
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Feb 27, 2026
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Isn’t that worth adding directly to clad? We have a pr that I believe I pinged you about vgvassilev/clad#1733
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The
digammafunction is important because it's the derivative of the log of the gamma function, which is widely used in likelihood fits because it appears in the Poisson distribution. If we want analytical Hessians for RooFit likelihoods - as promised in the ROOT plan of work -, we also need to provide the analytical derivative of the digamma function, which is the trigamma function. Fortunately, we can find it in the GNU scientific library:https://www.gnu.org/software/gsl/doc/html/specfunc.html#trigamma-function