Understanding allocations

General Usage
1

Hi,

I have troubles understanding why foo allocates whereas foo does not:

 1.623 ms (65804 allocations: 1.18 MiB)
  7.578 μs (0 allocations: 0 bytes)

Does someone know why?

Thank you,

using Parameters, BenchmarkTools

@with_kw mutable struct Mesh
	V = randn(100,110)
end

function foo1(V,g)
	Nw,Nv = size(V)
	for j=1:Nw
		for i=1:Nv
		gij  = g[j,i]
		gimj = (i > 1 )        ? g[j,i-1] : zero(gij)


		Fij  = (i > 1)         ? ((V[j,i]>=0.)   ? V[j,i]   * gimj : V[j,i]   * gij)  : zero(gij)

		end
	end
end


function foo(m,g)
	Nw,Nv = size(m.V)
	for j=1:Nw
		for i=1:Nv
		gij  = g[j,i]
		gimj = (i > 1 )        ? g[j,i-1] : zero(gij)

		Fij  = (i > 1)         ? ((m.V[j,i]>=0.)   ? m.V[j,i]   * gimj : m.V[j,i]   * gij)  : zero(gij)
		end
	end
end

V0 = rand(100,110)
g1 = randn(100,110)

m = Mesh()
@btime foo($m,$g1)
@btime foo1($(m.V),$g1)
2

Your Mesh isn’t strictly typed. Do:

@with_kw mutable struct Mesh
	V::Matrix{Float64} = randn(100,110)
end
1 Like
3

Well… thank you!