add overview

Author: rayegun

notebooks/PerformantSerialJulia.jl

@@ -47,6 +47,17 @@ VERSION
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+# ╔═╡ e611b52c-8d8c-41e8-a5d1-765c0d4306be
+md"""
+# What makes Julia code slow?
+
+### Type instability
+##### Type instability refers to a situation where the types of variables are *not* determined by the types of inputs, but instead by *values* of inputs.
+
+### Allocations
+##### Due to decisions in the standard libraries it is easy to accidentally allocate lots of memory, especially in hot loops. But this isn't *always* bad!
+"""
+
 # ╔═╡ 9331fad2-f29e-11eb-0349-477bd2e7e412
 md"""
 # Analysis toolbox
@@ -251,7 +262,7 @@ function matmul1(A, B)
 	m, p = size(A, 1), size(B, 2)
 	C = zeros(m, p)
 	for i = 1:m, j = 1:p
-		@views C[i, j] = sum(A[i, :] .* B[:, j])
+		C[i, j] = sum(A[i, :] .* B[:, j])
 	end
 	return C
 end
@@ -1013,7 +1024,8 @@ version = "17.4.0+2"
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