V_ideal=v*exp(p0*(v/p1)^p2/(1-v/p1)^0.25), where v=V_measured

//in the code it is
TF1 *fitf =new TF1("fitf","x*exp([0]*pow(x/[1],[2])/pow(1-x/[1],0.25))",0,15000);
fitf->SetParameters(10.0,8000.0,3.0);
tg->Fit("fitf");

FIT PARAMETERS

3910

1 p0 7.84428e-01 1.26830e-04 7.28546e-06 -1.38539e+00
2 p1 6.69371e+03 1.62013e-01 1.13919e-02 2.94718e-03
3 p2 2.53413e+00 3.55268e-04 8.36186e-05 2.96612e-01

3921

1 p0 7.24544e-01 8.28545e-05 7.17248e-06 8.09919e-01
2 p1 6.83027e+03 1.07837e-01 1.14919e-02 2.76049e-03
3 p2 2.32233e+00 3.06447e-04 9.93764e-05 2.96028e-01

3943

1 p0 6.30038e-01 3.85071e-05 9.57460e-06 -4.65559e+01
2 p1 6.65134e+03 4.44460e-02 1.34537e-02 2.19078e-02
3 p2 1.87528e+00 2.37580e-04 1.87942e-04 3.95142e+00

3947

1 p0 2.15697e+00 2.84533e-04 3.01447e-05 6.44027e+02
2 p1 8.56996e+03 1.54097e-01 2.00876e-02 -9.25111e-01
3 p2 4.17840e+00 1.87541e-04 9.95719e-05 -2.20325e+02

3911

1 p0 1.29907e+00 1.90360e-05 -1.46883e-06 -7.20478e+01
2 p1 6.94097e+03 7.29484e-03 -4.47529e-04 1.50924e-01
3 p2 3.70493e+00 1.00027e-04 -1.14213e-05 3.34110e+00

3914 (did not converge)

1 p0 7.33660e+00 2.99852e-05 -0.00000e+00 -1.28830e+09
2 p1 8.36192e+03 2.01833e-02 -0.00000e+00 1.52126e+07
3 p2 4.45949e+00 3.45593e-05 0.00000e+00 -2.39066e+10

3920


1 p0 2.32688e+00 4.48905e-05 0.00000e+00 -3.21786e+04
2 p1 7.16499e+03 1.12231e-02 0.00000e+00 1.02860e+02
3 p2 5.59589e+00 7.25050e-05 0.00000e+00 3.97604e+03

3926(did not converge)

1 p0 1.18105e+01 3.63824e-06 -0.00000e+00 5.23386e+05
2 p1 7.14511e+03 2.64464e-03 0.00000e+00 2.50646e+03
3 p2 1.08060e+01 3.00034e-05 -0.00000e+00 1.58418e+05


3929

1 p0 7.44752e+00 3.16269e-05 0.00000e+00 1.07229e+06
2 p1 8.36873e+03 6.33683e-03 -0.00000e+00 6.21349e+03
3 p2 7.11410e+00 4.88406e-05 0.00000e+00 1.12068e+05

3938

1 p0 1.49075e+00 1.58506e-05 3.86490e-05 -8.44264e+03
2 p1 8.01208e+03 5.33726e-03 1.73593e-02 3.96704e+01
3 p2 4.67917e+00 7.85702e-05 6.63801e-04 4.32874e+02

3944

1 p0 6.67532e+00 2.28441e-05 -0.00000e+00 1.01597e+07
2 p1 8.35620e+03 3.87689e-03 0.00000e+00 7.67223e+04
3 p2 1.02018e+01 7.11104e-05 -0.00000e+00 9.22395e+05

3913

p0= 3.85305e+00
p1= 9.06780e+03
p2= 3.50921e+00

3946

p0= 8.16909e-01
p1= 6.57001e+03
p2= 2.15528e+00

3928

p0= 7.97238e-01
p1= 6.61180e+03
p2= 2.26029e+00

3915

p0= 2.19046e+00
p1= 9.16965e+03
p2= 3.50490e+00