I suppose I could just use the getindex I supplied in the original post and
add a line or two that checks to see if length(tvp.mats)== 1. If it does,
then return that matrix.
Seems a bit clunky to me, but at least it is functional. Any thoughts?
On Thursday, November 13, 2014 10:24:44 AM UTC-5, Spencer Lyon wrote:
I am trying to construct a type with this definition:
>
> # are two ranges disjoint?
> isdisjoint(r1::UnitRange, r2::UnitRange) = isempty(intersect(r1, r2))
>
> # are a collection of ranges all disjoint?
> function all_disjoint(rs::UnitRange...)
> n = length(rs)
> for i=1:n, j=i+1:n
> if !(isdisjoint(rs[i], rs[j]))
> return false
> end
> end
> return true
> end
>
> type TimeVaryingParam{T<:Real, S<:Integer}
> mats::Vector{Matrix{T}}
> ranges::Vector{UnitRange{S}}
>
> function TimeVaryingParam(mats, ranges)
> if !(all_disjoint(ranges...))
> throw(ArugumentError("Ranges are overlapping"))
> end
> new(mats, ranges)
> end
> end
>
> function TimeVaryingParam{T<:Real, S<:Integer}(mats::Vector{Matrix{T}},
> ranges::Vector{UnitRange{S}})
> TimeVaryingParam{T, S}(mats, ranges)
> end
>
> # constructor of the form (mat, period_range), (mat2, period_range2)
> function TimeVaryingParam{T<:Real, S<:Integer}(input::(Matrix{T},
> UnitRange{S})...)
> mats = Matrix{T}[]
> ranges = UnitRange{S}[]
> for t in input
> push!(mats, t[1])
> push!(ranges, t[2])
> end
> TimeVaryingParam(mats, ranges)
> end
>
> function getindex(tvp::TimeVaryingParam, t::Int)
> # b/c all ranges are disjoint, ind has exactly zero or one elements
> ind = find(x->t in x, tvp.ranges)
> isempty(ind) && error("Invalid index. t=$t not in any supplied ranges")
> return tvp.mats[ind[1]]
> end
>
> The application is to be able to represent time-varying coefficient
> matrices of a linear state space system without having to make explicit
> copies of the matrices when they are the same for multiple periods.
>
> What I am trying to figure out is a convenient way for users to specify
> that a given matrix is the same for all periods. In other words, if the
> user was going to use the outer constructor I provided, I would like the
> following behavior to be true:
>
> a = [1 2; 3 4]
> tva = TimeVaryingParam((a, Colon()))
> t = rand(1:10000) # really just any integer
> tva[t] == a # returns true
>
> Now for the question/title of the post. I don’t know how : gets parsed in
> an indexing expression, so I don’t know how to enable this functionality.
> Can anyone help with this?
>
> Also, if someone has a better idea for how to enable this kind of
> functionality (i.e. an approach that doesn’t rely on Colon()) I am very
> happy to hear about it.
>
> Thanks!
>
>
