Vector of matrices vs. multidimensional arrays

General Usage Performance
3

Before anything else, read the Performance Tips–you shouldn’t work with non-constant variables in global scope.

using BenchmarkTools

# declare global-scope variables as constants, otherwise the compiler can't
# stably infer the variable's type
const L = 500 # integer literals in Julia don't require conversion
const v3 = [[rand(L) for i = 1:L] for j = 1:L]
const vec_mat = Array{Matrix}(L);
const arr = rand(L, L, L);

fill!(vec_mat, rand(L, L));

@btime v3 .+= 1.0
@btime vec_mat .+= 1.0
@btime arr .+= 1.0

  5.767 s (250500 allocations: 993.80 MiB)
  5.411 s (1000 allocations: 953.71 MiB)
  86.659 ms (0 allocations: 0 bytes)
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