Update README

Author: dlfivefifty

README.md

@@ -4,17 +4,140 @@
 [![codecov](https://codecov.io/gh/JuliaApproximation/InfiniteArrays.jl/branch/master/graph/badge.svg)](https://codecov.io/gh/JuliaApproximation/InfiniteArrays.jl)
 
 
-A Julia package for representing infinite-dimensional arrays
+A Julia package for representing infinite-dimensional arrays, designed to work
+with other array types. Infinite arrays are by necessity lazy, and so this
+package is closely linked to [LazyArrays.jl](https://github.com/JuliaArrays/LazyArrays.jl).
 
+The package currently supports construction, but future versions will include
+support for linear algebra operations like matrix multiplication, LU decompositions,
+and QR decompositions.
+
+
+Here are some examples of current functionality:
 
-This is a WIP package. When finished, the following behaviour should work:
 ```julia
-B = Ones(1,∞)  # creates 1 x ∞ InfMatrix of all ones
-T = diagm(Fill(0.5,∞)) + diagm(Fill(-0.5,∞),2)  # a Toeplitz operator
-e₁ = [1; Zeros(∞)]   # a PaddedInfVector
-(e₁*e₁')/2 # a PaddedInfMatrix: it knows to manipulate on the data
-C = T + (e₁*e₁')/2    # a PlusInfMatrix, it adds the rank-1 perturbation lazily
-D = diagm(1:∞,1)   # Chebyshev derivative, represented as a Diagonal{<:InfUnitRange}
-A = [B; D+C]   # A ConcatenatedInfMatrix
-u = A \ [2; Zeros(∞)]  # Finds Chebyshev coefficients of solution to u'+u = 0, u(1) = 2, using adaptive QR
-```
+julia> using InfiniteArrays, LinearAlgebra
+
+julia> x = Ones(∞) # infinite vector of all ones
+Ones{Float64,1,Tuple{InfiniteArrays.Infinity}} with indices OneToInf():
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ ⋮
+
+julia> cumsum(x) # infinite sum
+1.0:1.0:+∞
+
+julia> exp.(-(1:∞)) .+ 2 # broadcasting supported
+BroadcastArray{Float64,1,Base.Broadcast.Broadcasted{LazyArrays.LazyArrayStyle{1},Tuple{InfiniteArrays.OneToInf{Int64}},typeof(+),Tuple{BroadcastArray{Float64,1,Base.Broadcast.Broadcasted{LazyArrays.LazyArrayStyle{1},Tuple{InfiniteArrays.OneToInf{Int64}},typeof(exp),Tuple{InfiniteArrays.InfStepRange{Int64,Int64}}}},Int64}}} with indices OneToInf():
+ 2.3678794411714423
+ 2.135335283236613
+ 2.049787068367864
+ 2.018315638888734
+ 2.0067379469990856
+ 2.0024787521766663
+ 2.0009118819655547
+ 2.0003354626279024
+ 2.0001234098040865
+ 2.0000453999297623
+ 2.0000167017007904
+ 2.000006144212353
+ 2.000002260329407
+ 2.000000831528719
+ 2.0000003059023204
+ 2.0000001125351745
+ 2.0000000413993773
+ 2.00000001522998
+ 2.0000000056027964
+ 2.0000000020611535
+ 2.000000000758256
+ 2.0000000002789466
+ 2.000000000102619
+ 2.000000000037751
+ 2.000000000013888
+ 2.0000000000051092
+ ⋮
+
+julia> Diagonal(1:∞) # combines well with Base arrays
+Diagonal{Int64,InfiniteArrays.InfUnitRange{Int64}} with indices OneToInf()×OneToInf():
+ 1  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅  …
+ ⋅  2  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  3  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  4  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  5  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  6  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅  …
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  7  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  8  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  9   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  10   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅  11   ⋅   ⋅   ⋅   ⋅  …
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅  12   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅  13   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅  14   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅  15
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅  …
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅  …
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅
+ ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅  ⋅   ⋅   ⋅   ⋅   ⋅   ⋅   ⋅  …
+ ⋮              ⋮                ⋮                  ⋱
+
+ julia> C = cache(Ones(∞)); C[1] = 3; C # Use cache to make mutable
+LazyArrays.CachedArray{Float64,1,Array{Float64,1},Ones{Float64,1,Tuple{InfiniteArrays.Infinity}}} with indices OneToInf():
+ 3.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ 1.0
+ ⋮
+ ```