TMinuit の使い方 ref: http://qiita.com/pn11/items/36af3e3067f5d11f18eb

file0.txt

x^2+x

file1.cpp

#include <iostream>
#include <string>
using namespace std;

#include "TMinuit.h"

void chi2(Int_t &npar, Double_t *gin, Double_t &f, Double_t *par, Int_t iflag){
  f = par[0]*par[0] + par[0] + 1;
}

int main (){
  TMinuit *min = new TMinuit(1);
  min->SetPrintLevel(1);

  double par, parErr;
  string parName = "test_para";
  double stepSize = 0.1, minVal = -100.0, maxVal = 100.0;

  min->DefineParameter(0, parName.c_str(), par, stepSize, minVal, maxVal);

  min->SetFCN(chi2);

  int migrad_stats = min->Migrad();

  min->GetParameter(0, par, parErr);

  cout << "Result: " <<par << " +/- " << parErr << endl;
  cout << "Status of Migrad: " << migrad_stats << endl;

  delete min;

  return 0;
}

file2.txt

 **********
 **    1 **SET PRINT         100
 **********
 PARAMETER DEFINITIONS:
    NO.   NAME         VALUE      STEP SIZE      LIMITS
     1 test_para   2.10781e-317  1.00000e-01   -1.00000e+02  1.00000e+02
 **********
 **    2 **MIGRAD
 **********
 FIRST CALL TO USER FUNCTION AT NEW START POINT, WITH IFLAG=4.
 START MIGRAD MINIMIZATION.  STRATEGY  1.  CONVERGENCE WHEN EDM .LT. 1.00e-04
 FCN=1 FROM MIGRAD    STATUS=INITIATE        4 CALLS           5 TOTAL
                     EDM= unknown      STRATEGY= 1      NO ERROR MATRIX
  EXT PARAMETER               CURRENT GUESS       STEP         FIRST
  NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE
   1  test_para    0.00000e+00   1.00000e-01   1.00000e-03   1.00000e+02
NO ERROR MATRIX
 FCN=0.75 FROM MIGRAD    STATUS=PROGRESS        7 CALLS           8 TOTAL
                     EDM=1.74834e-11    STRATEGY= 1      NO ERROR MATRIX
  EXT PARAMETER               CURRENT GUESS       STEP         FIRST
  NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE
   1  test_para   -4.99998e-01   1.00000e-01  -5.00000e-03   4.18132e-04
 RELATIVE CHANGE IN COV. MATRIX= 50.0 per cent
 MIGRAD MINIMIZATION HAS CONVERGED.
 MIGRAD WILL VERIFY CONVERGENCE AND ERROR MATRIX.
   START COVARIANCE MATRIX CALCULATION.
 EIGENVALUES OF SECOND-DERIVATIVE MATRIX:
         1.0000e+00
 COVARIANCE MATRIX CALCULATED SUCCESSFULLY
 FCN=0.75 FROM MIGRAD    STATUS=CONVERGED      12 CALLS          13 TOTAL
                     EDM=8.74186e-12    STRATEGY= 1      ERROR MATRIX ACCURATE
  EXT PARAMETER                                   STEP         FIRST
  NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE
   1  test_para   -4.99998e-01   9.99983e-01   6.45935e-06   4.18130e-04
 EXTERNAL ERROR MATRIX.    NDIM=  25    NPAR=  1    ERR DEF=1
  1.000e+00
Result: -0.499998 +/- 0.999983
Status of Migrad: 0