假设我们想绘制函数 z = f(x, y) = cos(x + y) 的三维曲面图形，x 和 y 取值范围分别为 X 和 Y，则需要生成矩阵 ZZ，其中 ZZ[i, j] = f(X[i], Y[j]) = cos(X[i] + Y[j])，下面通过三种方式生成 ZZ：
# 仿照 meshgrid
function f()
X = 0:0.01:1
Y = 0:0.01:1
XX = repeat(X, 1, length(Y))
YY = repeat(Y', length(X), 1)
ZZ = cos.(XX .+ YY)
end
# 数组推导式
function g()
X = 0:0.01:1
Y = 0:0.01:1
ZZ = [cos(x + y) for x in X, y in Y]
end
# 广播
function h()
X = 0:0.01:1
Y = 0:0.01:1
ZZ = ((x, y) -> cos(x + y)).(X, Y')
end
在分别进行测试：
julia> @benchmark f()
BenchmarkTools.Trial:
memory estimate: 239.48 KiB
allocs estimate: 6
--------------
minimum time: 185.808 μs (0.00% GC)
median time: 213.422 μs (0.00% GC)
mean time: 241.130 μs (6.24% GC)
maximum time: 61.227 ms (99.50% GC)
--------------
samples: 10000
evals/sample: 1
julia> @benchmark g()
BenchmarkTools.Trial:
memory estimate: 79.83 KiB
allocs estimate: 2
--------------
minimum time: 133.725 μs (0.00% GC)
median time: 140.434 μs (0.00% GC)
mean time: 152.883 μs (6.26% GC)
maximum time: 59.987 ms (99.67% GC)
--------------
samples: 10000
evals/sample: 1
julia> @benchmark h()
BenchmarkTools.Trial:
memory estimate: 79.83 KiB
allocs estimate: 2
--------------
minimum time: 135.024 μs (0.00% GC)
median time: 140.200 μs (0.00% GC)
mean time: 157.678 μs (6.70% GC)
maximum time: 62.370 ms (99.69% GC)
--------------
samples: 10000
evals/sample: 1
可以看到类似于 meshgrid 的方式的开销是最大的，数组推导式和广播的方式则相差无几。