I'm a little bit surprised that eig can return either real or complex
results depending on the input values.
julia> eig([1.0 0.0; 0.0 1.0])
([1.0,1.0],
2x2 Array{Float64,2}:
-1.0 -0.0
-0.0 1.0)
julia> eig([1.0 1.0; -1.0 1.0])
([1.0 + 1.0im,1.0 - 1.0im],
2x2 Array{Complex{Float64},2}:
0.707107+0.0im 0.707107-0.0im
0.0+0.707107im 0.0-0.707107im)
Most other numerical functions in base have a return type that is a
function of the argument types only, not argument values. Is there a reason
eig is different?
