txt: ## dist_zef-FRITH-Math-Libgsl-Combination.md
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  # NAME
  
  Math::Libgsl::Combination - An interface to libgsl, the Gnu Scientific Library - Combinations.
  
  # SYNOPSIS
  
  ```
  use Math::Libgsl::Combination;
  
  ```
  
  # DESCRIPTION
  
  Math::Libgsl::Combination is an interface to the combination functions of libgsl, the Gnu Scientific Library.
  
  This package provides both the low-level interface to the C library (Raw) and a more comfortable interface layer for the Raku programmer.
  
  ### new(:$n!, :$k!)
  
  ### new($n!, $k!)
  
  The constructor accepts two parameters: the total number of elements in the set and the number of elements chosen from the set; the parameters can be passed as Pair-s or as single values. The combination object is already initialized in lexicographically first combination, i.e. (0, 1, 2, …, $k − 1).
  
  All the following methods *throw* on error if they return **self**, otherwise they *fail* on error.
  
  ### init(:$start? = TOP)
  
  This method initialize the combination object and returns **self**. The default is to initialize the object in lexicographically first combination, but by specifying the optional parameter **$start** as **BOTTOM** the initialization is performed in the lexicographically last combination, i.e. ($n − $k, $n − $k + 1, …, $n − 1). TOP and BOTTOM are declared as values of the Starting-point enum.
  
  ### copy($src! where \* ~~ Math::Libgsl::Combination)
  
  This method copies the combination **$src** into the current combination object and returns **self**.
  
  ### get(Int $elem! --> Int)
  
  This method returns the combination value at position **$elem**.
  
  ### all(--> Seq)
  
  This method returns a Seq of all the elements of the current combination.
  
  ### size(--> List)
  
  This method returns the (n, k) parameters of the current combination object.
  
  ### is-valid(--> Bool)
  
  This method checks whether the current combination is valid: the k elements should lie in the range 0 to $n − 1, with each value occurring once at most and in increasing order.
  
  ### next()
  
  ### prev()
  
  These functions advance or step backwards the combination and return **self**, useful for method chaining.
  
  ### bnext(--> Bool)
  
  ### bprev(--> Bool)
  
  These functions advance or step backwards the combination and return a Bool: **True** if successful or **False** if there's no more combination to produce.
  
  ### write(Str $filename! --> Int)
  
  This method writes the combination data to a file.
  
  ### read(Str $filename! --> Int)
  
  This method reads the combination data from a file. The combination must be of the same size of the one to be read.
  
  ### fprintf(Str $filename!, Str $format! --> Int)
  
  This method writes the combination data to a file, using the format specifier.
  
  ### fscanf(Str $filename!)
  
  This method reads the combination data from a file. The combination must be of the same size of the one to be read.
  
  # C Library Documentation
  
  For more details on libgsl see <https://www.gnu.org/software/gsl/>. The excellent C Library manual is available here <https://www.gnu.org/software/gsl/doc/html/index.html>, or here <https://www.gnu.org/software/gsl/doc/latex/gsl-ref.pdf> in PDF format.
  
  # Prerequisites
  
  This module requires the libgsl library to be installed. Please follow the instructions below based on your platform:
  
  ## Debian Linux and Ubuntu 20.04+
  
  ```
  sudo apt install libgsl23 libgsl-dev libgslcblas0
  
  ```
  
  That command will install libgslcblas0 as well, since it's used by the GSL.
  
  ## Ubuntu 18.04
  
  libgsl23 and libgslcblas0 have a missing symbol on Ubuntu 18.04. I solved the issue installing the Debian Buster version of those three libraries:
  
  * <http://http.us.debian.org/debian/pool/main/g/gsl/libgslcblas0_2.5+dfsg-6_amd64.deb>
  * <http://http.us.debian.org/debian/pool/main/g/gsl/libgsl23_2.5+dfsg-6_amd64.deb>
  * <http://http.us.debian.org/debian/pool/main/g/gsl/libgsl-dev_2.5+dfsg-6_amd64.deb>
  
  # Installation
  
  To install it using zef (a module management tool):
  
  ```
  $ zef install Math::Libgsl::Combination
  
  ```
  
  # AUTHOR
  
  Fernando Santagata [nando.santagata@gmail.com](mailto:nando.santagata@gmail.com)
  
  # COPYRIGHT AND LICENSE
  
  Copyright 2020 Fernando Santagata
  
  This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.
  