Merge pull request #8 from JuliaDiffEq/pkj-m-patch-3

Created matrix to graph conversion function

Author: ChrisRackauckas

src/matrix2graph.jl

@@ -0,0 +1,40 @@
+using SparseArrays
+include("custom_graph.jl")
+
+"""
+        matrix2graph(SparseMatrix)
+
+A utility function to generate a graph from input
+sparse matrix, columns are represented with vertices
+and 2 vertices are connected with an edge only if
+the two columns are mutually orthogonal.
+"""
+function matrix2graph(SparseMatrix::SparseMatrixCSC{Int64,Int64})
+    dropzeros(SparseMatrix)
+    (rows_index, cols_index, val) = findnz(SparseMatrix)
+
+    V = col = size(SparseMatrix, 2)
+    row = size(SparseMatrix, 1)
+
+    vertices = zeros(Int64, 0)
+    edges = [Vector{Int64}() for _ in 1:V]
+
+    graph = CGraph(vertices, edges)
+    for i = 1:V
+        push!(vertices, i)
+    end
+
+    for i = 1:length(cols_index)
+        cur_col = cols_index[i]
+        for j = 1:(i-1)
+            next_col = cols_index[j]
+            if cur_col != next_col
+                if row_index[i] == row_index[j]
+                    #add edge
+                    add_edge!(graph, i, j)
+                end
+            end
+        end
+    end
+    return graph
+end