I am trying to perform a fit to an exponential plus a polynomial. I get some good quick results using gnuplot. Which are the values found inside the `initialParams`

found inside the C-macro.

If I set those as the initial parameters and let all the fit parameters run free, I do not get really good results.

Then, I decide to fix some limits to the exponential parameters, using:

```
fn->SetParLimits(0,0.8*initialParams[0],1.2*initialParams[0]);
fn->SetParLimits(1,0.8*initialParams[1],1.2*initialParams[1]);
```

You will see those lines commented inside the C-macro. It is a bit strange that I observe in the fitting results the following:

```
p0 = -9.25005e-06 (fixed)
p1 = 0.00186612 +/- 7.44872e-09 (limited)
```

Although I just limited and not fixed parameter `p0`

.

The result seems a bit better although not perfect in all the range.

If I fix the two exponential parameters then I get the result I expect, even if I let free the polynomial parameters:

I really need to automatize this process for similar curves, so I need to solve this problem. The biggest suspect for me is why the *p0* parameter is fixed even if I just used `SetParLimits`

.

BxFit_0.C (2.4 KB)

outFinal_Xp.txt (16.2 KB)