[Minuit2] Only compute global correlation matrix when needed #18978
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Test Results 21 files 21 suites 3d 14h 15m 20s ⏱️ Results for commit 6d18080. ♻️ This comment has been updated with latest results. |
guitargeek
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The plan is to update the minimizer implementations to not compute the global correlations unconditionally anymore, but only when the user actually requests them with `GlobalCC()`. For this, it makes more sense to return all values at once. Otherwise, we would have to implement some caching, which is not desirable.
This makes the code less error prone, because initialization can't be forgotten or be inconsistent between constructors.
For many parameters, the global correlation matrix can be very expensive to compute. We therefore don't want to calculate it unconditionally, but only when the user actually requests them by calling `Minimizer::GlobalCC()`.
lmoneta
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Oct 3, 2025
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The function
double ROOT::Math::Minimizer::GlobalCC(unsigned int ivar)was changed tostd::vector<double> ROOT::Math::Minimizer::GlobalCC(), always returning the full list of global correlations.This change was needed because global correlations are not unconditionally computed and cached in the minimizer anymore. Only computing them when calling
GlobalCC()avoids unneeded overhead when global correlations are not required.