HOPPET 2.1.1

HOPPET: A Higher Order Perturbative Parton Evolution Toolkit

HOPPET: A Higher Order Perturbative Parton Evolution Toolkit

HOPPET is a package for carrying out DGLAP evolution and other common manipulations of parton distribution functions (PDFs) in particle physics. The core package is written in Fortran. This Python interface provides access to a key subset of the functionality, the part known in the documentation as the "streamlined" interface.

The full underlying code and documentation can be found at https://github.com/hoppet-code/hoppet.

Example usage

import hoppet as hp
import numpy as np

def main():
    # choose the underlying spacing in y=log(1/x): 
    # smaller spacing gives higher accuracy but slower evolution
    dy = 0.1  
    # choose NNLO evolution
    nloop = 3 
    # Start hoppet
    hp.Start(dy, nloop)
    
    asQ0 = 0.35
    Q0 = np.sqrt(2.0)
    # Do the evolution starting from a standard benchmark initial condition 
    hp.Evolve(asQ0, Q0, nloop, 1.0, hp.BenchmarkPDFunpol, Q0)

    # Evaluate the PDFs at some x values and print them
    xvals = [1e-5,1e-4,1e-3,1e-2,0.1,0.3,0.5,0.7,0.9]
    Q = 100.0

    print('')
    print('           Evaluating PDFs at Q =',Q, ' GeV')
    print('    x      u-ubar      d-dbar    2(ubr+dbr)    c+cbar       gluon')
    for ix in range(9):
        pdf_array = hp.Eval(xvals[ix], Q)
        print('{:7.1E} {:11.4E} {:11.4E} {:11.4E} {:11.4E} {:11.4E}'.format(
            xvals[ix],
            pdf_array[6 + 2] - pdf_array[6 - 2], 
            pdf_array[6 + 1] - pdf_array[6 - 1], 
            2 * (pdf_array[6 - 1] + pdf_array[6 - 2]),
            pdf_array[6 - 4] + pdf_array[6 + 4],
            pdf_array[6 + 0]
        ))

    hp.DeleteAll()

For more examples take a look at example_py. The above example is essentially identical to tabulation_example.py and prints the output of a typical benchmark PDF.

Citation policy

If you use this program in a scientific publication we ask that you cite

G.P. Salam, J. Rojo, 'A Higher Order Perturbative Parton Evolution Toolkit (HOPPET)', Comput. Phys. Commun. 180 (2009) 120-156, arXiv:0804.3755

and

A. Karlberg, P. Nason, G.P. Salam, G. Zanderighi & F. Dreyer arXiv:2510.09310.