fix-diag to sparse conversion (#21)

* fix-diag to sparse conversion

* fix

* fix typo

Author: GiggleLiu

src/conversions.jl

@@ -19,6 +19,11 @@ function SparseMatrixCSC(M::PermMatrix)
     SparseMatrixCSC(n, n, collect(1:n+1), order, M.vals[order])
 end
 
+function SparseMatrixCSC(D::Diagonal{T}) where T
+    m = length(D.diag)
+    return SparseMatrixCSC(m, m, Vector(1:(m+1)), Vector(1:m), Vector{T}(D.diag))
+end
+
 SparseMatrixCSC{Tv, Ti}(M::PermMatrix{Tv, Ti}) where {Tv, Ti} = SparseMatrixCSC(M)
 SparseMatrixCSC(coo::SparseMatrixCOO) = sparse(coo.is, coo.js, coo.vs, coo.m, coo.n)