Function Reference
First-order differences
whittaker1(input::Vector{Float64}, weights::Vector{T <: Number}, lambda::Float64) -> z::Vector{Float64} whittaker1!(input::Vector{Float64}, weights::Vector{T <: Number}, lambda::Float64)
Second-order differences
whittaker2(input::Vector{Float64}, weights::Vector{T <: Number}, lambda::Float64) -> z::Vector{Float64} whittaker2!(input::Vector{Float64}, weights::Vector{T <: Number}, lambda::Float64)