Quickstart

The following sections only cover the first steps and the reader is refered to the official Recola manuals which describes all aspects of the libraries. The docs serves as a work of reference.

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Demo files

Running demo files

The Recola and Recola2 library come with several demo files located in recola-1.4.4/demos and recola2-2.2.4/demos, respectively.

The demo files illustrate the usage from the basic features (demo0) to specifc features (e.g. computation of colour-correlations in demo3). The small introduction to each demo-file can be found in the official manuals.

The demo files come in three languages, namely Fortran95, C++ and Python 1. The Fortran95 and C++ demo files can be run by invoking the run script:

./run <demofile>

where <demofile> can be demoi_rcl, cdemoi_rcl (\(i=0,1,\ldots\)).

The python demo files can be run directly via:

python <demofile>

where <demofile> taking the values pydemoi_rcl (\(i=0,1,\ldots\)).

1

The Python interface is only available in Recola2.

Minimal demo file

Computations in Recola follow the strict order:

1. Process definition

2. Process generation

3. Process computation

Python

Fortran

C++

from pyrecola import *

# define a simple 2 -> 4 process
define_process_rcl(1, 'u u~ -> d d~ g g', 'NLO')

# generate it
generate_processes_rcl()

# generate a sample PSP using RAMBO
p1 = [500., 0., 0., 500.]
p2 = [500., 0., 0., -500.]
psp = set_outgoing_momenta_rcl(1, [p1, p2])

# compute tree squared and tree one-loop interference
A0, A1, _ = compute_process_rcl(1, psp, 'NLO')

use recola

implicit none
integer, parameter :: dp = kind (23d0)
real(dp) :: p(0:3,1:6), A2(2)

! define a simple 2 -> 4 process
call define_process_rcl(1, 'u u~ -> d d~ g g', 'NLO')

! generate it
call generate_processes_rcl

! generate a sample PSP using RAMBO
p(:,1) = [500d0, 0d0, 0d0,  500d0]
p(:,2) = [500d0, 0d0, 0d0, -500d0]
call set_outgoing_momenta_rcl(1, p(:,1:2), p)

! compute tree squared and tree one-loop interference
call compute_process_rcl(1, psp, 'NLO', A2)

#include "recola.hpp"

// define a simple 2 -> 4 process
Recola::define_process_rcl(1, "u u~ -> d d~ g g", "NLO");

// generate it
Recola::generate_processes_rcl();

// generate a sample PSP using RAMBO
double pin[2][4] =
{{500., 0., 0., 500.},
 {500., 0., 0., -500.}};
double psp[6][4];
Recola::set_outgoing_momenta_rcl(1, pin, psp);

// compute tree squared and tree one-loop interference
double A2[2];
Recola::compute_process_rcl(1, psp, "NLO", A2);

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Custom demo files

The demo files can be modified and manipulated at will. Adding new demo files requires to follow the naming conventions:

• Fortran95: demo*_rcl.f90,

• C++: cdemo*_rcl.cpp,

otherwise sources will not be added to the list of executables by the CMake configuration. Here, the * is a wildcard accepting arbitrary character strings. In order to compile newly added source files a reconfiguration of the Recola/Recola2 library is required. To this end, switch to the build folder and run:

cmake [options] ..

Alternatively, the Recola2 library can be used in an external project as exemplified in recola2-collier-2.2.4 in project_cmake/CMakeLists.txt (see also the official manual).

Setting up Python demo files is straightforward, i.e. without restrictions concerning naming conventions of demo files.