RFC: Add vector partitions functionality

[Stivanification]

This is a julia port of the sage VectorPartitions function originally written by Amritanshu Prasad (2013).

A vector partition of "vector" is a list of vectors with non-negative integer entries whose sum is "vector". The method vector_partitions creates all vector partitions of "vector" with all parts greater than or equal to "min" in lexicographic order recursively. The function expects an Int64-Array "vector" as first argument and an optional Int64-Array "min" as second argument.

If "min" is not specified, then the class of all vector partitions of "vector" is created:

  julia> vector_partitions([2, 2])
         9-element Array{Any,1}:
         Array{Int64,1}[[1,0],[1,0],[0,1],[0,1]]
         Array{Int64,1}[[2,0],[0,1],[0,1]]
         Array{Int64,1}[[1,1],[1,0],[0,1]]
         Array{Int64,1}[[2,1],[0,1]]
         Array{Int64,1}[[1,0],[1,0],[0,2]]
         Array{Int64,1}[[2,0],[0,2]]
         Array{Int64,1}[[1,2],[1,0]]
         Array{Int64,1}[[1,1],[1,1]]
         Array{Int64,1}[[2,2]]

If "min" is specified, then the array lists those vector partitions whose parts are all greater than or equal to "min" in lexicographic order:

   julia> vector_partitions([2,2],[1,0])
          3-element Array{Any,1}:
          Array{Int64,1}[[1,2],[1,0]]
          Array{Int64,1}[[1,1],[1,1]]
          Array{Int64,1}[[2,2]]

[codecov-io]

Codecov Report

Merging #43 into master will decrease coverage by -5.4%. The diff coverage is 0%.

@@            Coverage Diff            @@
##           master      #43     +/-   ##
=========================================
- Coverage   96.96%   91.57%   -5.4%     
=========================================
  Files           6        7      +1     
  Lines         594      629     +35     
=========================================
  Hits          576      576             
- Misses         18       53     +35

Impacted Files	Coverage Δ
src/vector_partitions.jl	0% <ø> (ø)

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[Stivanification]

Hm I seem to get code coverage of 0.0 which doesn't seem right at all...

[mschauer]

I am going through stalled pull requests of this repo. If you have time and interest to update this, I'm going to review and merge.