I've been having a minor problem with a fitting macro I've been writing. I wanted to include an option to set a constant to zero, but it's not working. I can illustrate the problem with this test macro: { Float_t exconst; Float_t x[5], y[5], xe[5], ye[5]; for(int l=0;l<5;l++){ x[l]=l; y[l]=11*pow(l,2)-330*l+2500; xe[l]=.2; ye[l]=2.5; } // define fit function // TF1 *e1 = new TF1("e1","[0]*x+[1]",.5,15); // set guess parameters // e1.SetParameter(0,2000); e1.SetParameter(1,1); printf("Enter constant: "); scanf("%f",&exconst); e1.SetParLimits(1,exconst,exconst); e1.SetParameter(1,exconst); gre = new TGraphErrors(5,x,y,xe,ye); gre.Fit("e1"); } The macro will fix parameter 1 properly for any entered value except zero. If zero is entered, it fits parameter 1. (At least in Root Version 2.21/08.) By the way, thanks for the help with the download. -Matt Fritts
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