SIO is the type for singular integral operators.

DiscreteSIO(SIO::SIO; h_mesh::Real, h_quad::Real, h_quad_diag::Real)

is the constructor for a discretisation of a singular integral operator, 'SIO'. hmesh is the meshwidth parameter for the discretisation of the underlying fractal hquad denotes the discretisation parameter for the integrals in the stiffness matrix. hquaddiag is the parameter used to compute the diagonal elements of the matrix