eigenvalues of interval matrices

[lucaferranti]

Feature description

Implement the algorithms described in this paper to find a bound on eigenvalue set of interval matrices

Minimum working example

I'm thinking of an interface like:

function eigvals(A::AbstractMatrix{IntervalOrComplexInterval}, method=someDefaultMethod)
  .....
end

function eigvals(A::SymmetricMatrix{IntervalOrComplexInterval}, method=someDefaultMethodForSymmetricMatrices)
....
end

For start the methods could be

• Rohn method for symmetric matrices
• Herz method for symmetric matrices (has exponential complexity, maybe later, would probably benefit from list_orthants should return an iterator #76)
• Rohn method for general real matrices
• Hladík method for general compex matrices

In a first version, it could be non-rigorous (solve real symmetric eigenvalue problems with eigen). Later, it could have rigorous and non-rigorous version (after #68 is merged)

Additional information