MultiDimFit Print method.

From: Marcos Gimenez <margial_at_ific.uv.es>
Date: Mon, 11 Jul 2005 20:48:51 +0200

Hello all

After making a succesfull fit using the MultiDimFit class, i printed the output function using fit->Print("m"); and i found that there were diferences in the powers shown between fit->Print("m") and fit->Print("c");

Using Print("m") (bad results after testing the fit)

Parameterization:

---

  Normalised variables:

        y_0     = 1 + 2 * (x_0 - 1) / (1 - -1)
        y_1     = 1 + 2 * (x_1 - 1) / (1 - -1)

  f(y_0, y_1) = 0.6374


        + 28.69 * y_0

        - 0.4414 * y_0^3


        + 0.005439 * y_0 * y_1^3

        + 14.73 * y_0^4

        + 19.87 * y_1^5

        + 0.5973 * y_0^3 * y_1^3

        - 0.1731 * y_0^5
        - 22.42 * y_0^6
        - 17.31 * y_1^7


        + 0.2964 * y_1

        - 3.186 * y_1^3
        - 0.2975 * y_1^4

Using Print("c") (good results after testing the fit, same results when using fit->Eval(x) method)

Coefficients:

---

   # Value Error Powers

---

   0        0.6374        0.3363     0   0
   1         28.69         1.419     1   0
   2       -0.4414         2.462     2   0
   3      0.005439        0.8616     1   2
   4         14.73         10.56     3   0
   5         19.87          75.6     0   4
   6        0.5973         1.171     2   2
   7       -0.1731         2.452     4   0
   8        -22.42         9.288     5   0
   9        -17.31         65.37     0   6
  10        0.2964          0.63     0   1
  11        -3.186         10.77     0   2
  12       -0.2975        0.7781     0   3

If i look in the TMultiDimFit source and i search what it does when "m" option it is selected there is a part in the code after the switch(fPolyType) that i think it should be using p-1 instead of p, because TMultiDimFit stores power+1.

Now

      for (Int_t j = 0; j < fNVariables; j++) {
        Int_t p = fPowers[fPowerIndex[i] * fNVariables + j];
        switch (p) { 
        case 1: break;
        case 2: cout << " * y_" << j; break;
        default:
          switch(fPolyType) {
          case kLegendre:  cout << " * L_" << p << "(y_" << j << ")"; break;
          case kChebyshev: cout << " * C_" << p << "(y_" << j << ")"; break;
          default:         cout << " * y_" << j << "^" << p; break;
          }
        }
                          
      }

I think it should be

      for (Int_t j = 0; j < fNVariables; j++) {
        Int_t p = fPowers[fPowerIndex[i] * fNVariables + j];
        switch (p) { 
        case 1: break;
        case 2: cout << " * y_" << j; break;
        default:
          switch(fPolyType) {
          case kLegendre:  cout << " * L_" << p-1 << "(y_" << j << ")"; break;
          case kChebyshev: cout << " * C_" << p-1 << "(y_" << j << ")"; break;
          default:         cout << " * y_" << j << "^" << p-1; break;
          }
        }
                          
      }

 Anyway i am not really really sure of that.

I am using ROOT 4.02 but i looked also at 5.02/00 source to be sure and i found the same.

Thank you

Marcos Received on Mon Jul 11 2005 - 20:49:04 MEST