[hist] Fix TFormula Hessian result sizing - #22877
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guitargeek merged 1 commit intoJul 28, 2026
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HessianPar writes fNpar * fNpar entries, but its CladStorage overload only resized results smaller than fNpar. For two or more parameters, a partially sized result could pass the check and leave Clad writing past the vector's size. Check for the full flattened Hessian size and cover the missed case in ResultUpsize.
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Hi! Thanks for the PR! How did you get interested in fixing this? Are you a user of ROOT, TFormula, or Clad? |
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Hi @guitargeek, I’m not a user yet. I’d been reading about CERN, and ROOT kept coming up, so I started exploring the code. In HessianPar, I noticed the size check used fNpar even though the Hessian result needs fNpar * fNpar entries. A two-parameter case exposed the mismatch. |
Test Results 18 files 18 suites 3d 10h 22m 25s ⏱️ For more details on these failures, see this check. Results for commit b0fe66b. |
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TFormula::HessianParreturns a flattened matrix withfNpar * fNparelements, but the
CladStorageoverload only resized results smallerthan
fNpar. With two parameters, a two-element result passed the oldcheck even though the Hessian needs four elements.
Use the full Hessian size for the check and update the existing
ResultUpsizetest to cover this case.