# @inbounds with dot notation?

**URL:** <https://discourse.julialang.org/t/inbounds-with-dot-notation/4939>\
**Category:** General Usage\
**Tags:** performance\
**Created:** [July 18, 2017, 11:42pm UTC](https://discourse.julialang.org/t/inbounds-with-dot-notation/4939 "2017-07-18T23:42:05Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![dpo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dpo/32/3335_2.png) [@dpo](https://discourse.julialang.org/u/dpo)\
**Post date:** [July 18, 2017, 11:42pm UTC](https://discourse.julialang.org/t/inbounds-with-dot-notation/4939/1 "2017-07-18T23:42:06Z")

</div>

I’m wondering how to use `@inbounds` when vectorizing a function with dot notation or `@.`. I found `Base.@propagate_inbounds` but am not sure I’m using it correctly. Consider

```julia
using BenchmarkTools

Base.@propagate_inbounds active_dot(x, l, u, δ) = (x ≤ l + δ) || (x ≥ u - δ)

function active!(A, x, l, u, δ)
  @inbounds for i in eachindex(x)
    A[i] = (x[i] ≤ l[i] + δ[i]) || (x[i] ≥ u[i] - δ[i])
  end
  A
end

function foo(n)
  l = zeros(n)
  u = ones(n)
  x = rand(n) - 0.5
  rtol = atol = 1.0e-8
  # is it possible to write the following with dot notation??
  δ = [-Inf < l[i] < u[i] < Inf ? min(rtol * (u[i] - l[i]), atol) : atol for i = 1:n]

  A1 = Array{Bool}(n)
  A2 = Array{Bool}(n)

  t1 = @benchmark active!($A1, $x, $l, $u, $δ)
  show(STDOUT, MIME"text/plain"(), t1); println()

  t2 = @benchmark $A2 .= active_dot.($x, $l, $u, $δ)
  show(STDOUT, MIME"text/plain"(), t2); println()

  @assert all(A1 .== A2)
end

foo(10000)

```

The explicit `@inbounds`-instrumented loop is still about 10x faster:

```julia
BenchmarkTools.Trial: 
  memory estimate: 0 bytes
  allocs estimate: 0
  --------------
  minimum time: 5.528 μs (0.00% GC)
  median time: 6.125 μs (0.00% GC)
  mean time: 6.545 μs (0.00% GC)
  maximum time: 23.742 μs (0.00% GC)
  --------------
  samples: 10000
  evals/sample: 6
BenchmarkTools.Trial: 
  memory estimate: 0 bytes
  allocs estimate: 0
  --------------
  minimum time: 45.809 μs (0.00% GC)
  median time: 49.291 μs (0.00% GC)
  mean time: 52.758 μs (0.00% GC)
  maximum time: 229.375 μs (0.00% GC)
  --------------
  samples: 10000
  evals/sample: 1

```

Can `active_dot` be improved somehow to close the gap? Thanks!