outputsize(m, inputsize::Tuple; padbatch=false)

Calculate the size of the output from model m, given the size of the input. Obeys outputsize(m, size(x)) == size(m(x)) for valid input x.

Keyword padbatch=true is equivalent to using (inputsize..., 1), and returns the final size including this extra batch dimension.

This should be faster than calling size(m(x)). It uses a trivial number type, which should work out of the box for custom layers.

If m is a Tuple or Vector, its elements are applied in sequence, like Chain(m...).

Examples

			julia> using Flux: outputsize

julia> outputsize(Dense(10, 4), (10,); padbatch=true)
(4, 1)

julia> m = Chain(Conv((3, 3), 3 => 16), Conv((3, 3), 16 => 32));

julia> m(randn(Float32, 10, 10, 3, 64)) |> size
(6, 6, 32, 64)

julia> outputsize(m, (10, 10, 3); padbatch=true)
(6, 6, 32, 1)

julia> outputsize(m, (10, 10, 3, 64))
(6, 6, 32, 64)

julia> try outputsize(m, (10, 10, 7, 64)) catch e println(e) end
┌ Error: layer Conv((3, 3), 3=>16), index 1 in Chain, gave an error with input of size (10, 10, 7, 64)
└ @ Flux ~/.julia/dev/Flux/src/outputsize.jl:114
DimensionMismatch("Input channels must match! (7 vs. 3)")

julia> outputsize([Dense(10, 4), Dense(4, 2)], (10, 1)) # Vector of layers becomes a Chain
(2, 1)

			outputsize(m, x_size, y_size, ...; padbatch=false)

For model or layer m accepting multiple arrays as input, this returns size(m((x, y, ...))) given size_x = size(x), etc.

Examples

			julia> x, y = rand(Float32, 5, 64), rand(Float32, 7, 64);

julia> par = Parallel(vcat, Dense(5, 9), Dense(7, 11));

julia> Flux.outputsize(par, (5, 64), (7, 64))
(20, 64)

julia> m = Chain(par, Dense(20, 13), softmax);

julia> Flux.outputsize(m, (5,), (7,); padbatch=true)
(13, 1)

julia> par(x, y) == par((x, y)) == Chain(par, identity)((x, y))
true

Notice that Chain only accepts multiple arrays as a tuple, while Parallel also accepts them as multiple arguments; outputsize always supplies the tuple.