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[hist] Always use maximum floating point precision in GetExpFormula #19734

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Merged
merged 1 commit into from
Aug 26, 2025
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[hist] Always use maximum floating point precision in GetExpFormula #19734

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2 changes: 1 addition & 1 deletion hist/hist/inc/TFormula.h
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Original file line number Diff line number Diff line change
Expand Up @@ -248,7 +248,7 @@ class TFormula : public TNamed
#ifdef R__HAS_VECCORE
ROOT::Double_v EvalParVec(const ROOT::Double_v *x, const Double_t *params = nullptr) const;
#endif
TString GetExpFormula(Option_t *option = "", const char *fl_format = "%g") const;
TString GetExpFormula(Option_t *option = "") const;
TString GetGradientFormula() const;
TString GetHessianFormula() const;
TString GetUniqueFuncName() const {
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40 changes: 25 additions & 15 deletions hist/hist/src/TFormula.cxx
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Expand Up @@ -23,12 +23,14 @@
#include "ROOT/StringUtils.hxx"

#include <array>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <memory>
#include <unordered_map>
#include <functional>
#include <set>
#include <sstream>
#include <unordered_map>

using std::map, std::pair, std::make_pair, std::list, std::max, std::string;

Expand All @@ -39,6 +41,17 @@ using std::map, std::pair, std::make_pair, std::list, std::max, std::string;

ClassImp(TFormula);

namespace {

std::string doubleToString(double val)
{
std::stringstream ss;
ss << std::setprecision(std::numeric_limits<double>::max_digits10) << val;
return ss.str();
}

} // namespace

/** \class TFormula TFormula.h "inc/TFormula.h"
\ingroup Hist
The Formula class
Expand Down Expand Up @@ -2341,8 +2354,7 @@ void TFormula::ProcessFormula(TString &formula)
map<TString, Double_t>::iterator constIt = fConsts.find(fun.GetName());
if (constIt != fConsts.end()) {
TString pattern = TString::Format("{%s}", fun.GetName());
TString value = TString::Format("%lf", (*constIt).second);
formula.ReplaceAll(pattern, value);
formula.ReplaceAll(pattern, doubleToString(constIt->second));
fun.fFound = true;
// std::cout << "constant with name " << fun.GetName() << " is found " << std::endl;
continue;
Expand Down Expand Up @@ -3606,12 +3618,8 @@ void TFormula::ReInitializeEvalMethod() {
/// - If option = "P" replace the parameter names with their values
/// - If option = "CLING" return the actual expression used to build the function passed to cling
/// - If option = "CLINGP" replace in the CLING expression the parameter with their values
/// @param fl_format specifies the printf floating point precision when option
/// contains "p". Default is `%g` (6 decimals). If you need more precision,
/// change e.g. to `%.9f`, or `%a` for a lossless representation.
/// @see https://cplusplus.com/reference/cstdio/printf/

TString TFormula::GetExpFormula(Option_t *option, const char *fl_format) const
TString TFormula::GetExpFormula(Option_t *option) const
{
TString opt(option);
if (opt.IsNull() || TestBit(TFormula::kLambda) ) return fFormula;
Expand Down Expand Up @@ -3647,9 +3655,10 @@ TString TFormula::GetExpFormula(Option_t *option, const char *fl_format) const
TString parNumbName = clingFormula(i+2,j-i-2);
int parNumber = parNumbName.Atoi();
assert(parNumber < fNpar);
TString replacement = TString::Format(fl_format, GetParameter(parNumber));
clingFormula.Replace(i,j-i+1, replacement );
i += replacement.Length();
std::stringstream ss;
std::string replacement = doubleToString(GetParameter(parNumber));
clingFormula.Replace(i,j-i+1, replacement);
i += replacement.size();
}
i++;
}
Expand All @@ -3669,9 +3678,10 @@ TString TFormula::GetExpFormula(Option_t *option, const char *fl_format) const
return expFormula;
}
TString parName = expFormula(i+1,j-i-1);
TString replacement = TString::Format(fl_format, GetParameter(parName));
expFormula.Replace(i,j-i+1, replacement );
i += replacement.Length();
std::stringstream ss;
std::string replacement = doubleToString(GetParameter(parName));
expFormula.Replace(i,j-i+1, replacement);
i += replacement.size();
}
i++;
}
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2 changes: 1 addition & 1 deletion test/TFormulaParsingTests.h
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Expand Up @@ -308,7 +308,7 @@ bool test16() {
// test GetExpFormula
TFormula f("f","[2] + [0]*x + [1]*x*x");
f.SetParameters(1,2,3);
return (f.GetExpFormula("CLING P", "%f") == TString("3.000000+1.000000*x[0]+2.000000*x[0]*x[0] "));
return (f.GetExpFormula("CLING P") == TString("3+1*x[0]+2*x[0]*x[0] "));
}

bool test17() {
Expand Down
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