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Description of .LHgrid files

All text strings must be enclosed in single quotation marks.

The example shown here is from the MRST2002nlo.LHgrid file


The first line declares the earliest version of LHAPDF with which the files works, in the following way: 'Version' '5.3'
Next follows a section giving a description of the PDF set. It starts with the line 'Description:' followed by an arbitrary (max 20) number of lines. This is the text that is printed out with the call description() command. 'Description:'
'MRST fit: hep-ph/0211080'
'This set has 1 member PDFs.'

Next is a section, starting with the line 'Alphas:', describing how Alphas is to be calculated. It is followed by two lines. The three parameters of the first of these lines declare (1) either Variable or Fixed depending on whether or not Alphas is allowed to vary with Q**2, (2) the order of alphas lo, nlo or nnlo, and (3) the method used in calculating Alphas, either Internal, Evolcode, MRSTalfa or CTEQalfa. Internal uses code in the LHAPDF programme, Evolcode uses code specific to the evolution package, and the final two use the specific Alphas codes of MRST and CTEQ respectively. The third line sets various numerical values used in the Alphas calculation. The first parameter of this line defines Lambda_QCD either as the parameter number in the 'Parameterlist:' (see later) or for the case of 'Fixed' Alphas, the actual value of Lambda_QCD. The second parameter is mass(Z0)**2, and the remaining three are the masses of the charm, bottom and top quarks. 'Alphas:'
'Variable','nlo','EvolCode'
1,91.118,1.43,4.30,180.0

The next small section, starting with the line 'MinMax:', gives the maxima and minima of x and Q**2 respectively for each data set. These values are used for information only and not used explicitly in the PDF determination. The second line gives (1) the number of PDF sets and (2) either 1 or 0 depending on whether the same values or different ones are given for each set. The third line (and others if indivdual values are given for each set) gives the values. Note that as in the Parameterlist the default set 0 has to be included in the list. 'MinMax:'
1,1
1.E-05,1.,1.25,10000000.

The next small section, starting with the line 'QCDparams:', gives LAMBDA_QCD4 and LAMBDA_QCD5 for each data set. These values are used for information only and not used explicitly in the PDF determination. The second line gives (1) the number of PDF sets and (2) either 1 or 0 depending on whether the same values or different ones are given for each set. The third line (and others if indivdual values are given for each set) gives LAMBDA_QCD4 and LAMBDA_QCD5. Note that as in the Parameterlist the default set 0 has to be included in the list. 'QCDparams:'
1,1
0.334,0.233

The next small section, starting with the line 'Parameterlist:', gives and parameters which need to be read in. In this case the parameter is alphas. The second line gives (1) the number of PDF sets and (2) the number of parameters. The third line (and others if indivdual values are given for each set) gives The actual values. Note that the in the the default set 0 has to be included in the list. 'Parameterlist:'
'list',1,1
0.119701
0.119701

The final large section starting with the line 'Evolution:' defines the evolution method used in the fit and input the interpolation grid values. The first line has three parameters which are (1) the order of the fit (in this case nlo), rthe Q**2 in GeV**2 at which the fit was made, and the renormalization factor which is set to 1.0 for all sets. The next line, in this case MRSTgrid, defines the type of evolution to be used in the program. Here 'MRSTgrid' defines interpolation using the MRST interpolation code. Following this is the actuasl gid which is read into the program for use in producing the PDFs. 'Evolution:'
'nlo',1.0,1.0
'MRSTgrid'
1,0
0.00949 0.00208 -8.77372 0.89445 0.00000 0.00000 0.43318 0.89446
0.00964 0.00215 -8.32812 0.87515 0.00000 0.00000 0.41881 0.87515
0.00987 0.00224 -7.02499 0.87250 0.00466 0.00000 0.42304 0.87251
....
....
....
0.00006 0.00001 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000
0.00006 0.00001 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000
0.00005 0.00001 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000

The end of the file it defined by the line 'End' 'End:'