ScaledNumbersInput

Provides the @SI macro for converting numbers with SI prefixes

Examples

julia> @SI 4.5T
4.5e12

julia> @SI values = [1.2n, 100a, 5.7G]
3-element Vector{Float64}:
 1.2e-9
 1.0e-16
 5.7e9

Supported Scaling Factors

The following scaling factors are recognized:

Scaling Symbol	Factor
Y	1e24
Z	1e21
E	1e18
P	1e15
T	1e12
G	1e9
M	1e6
K	1e3
k	1e3
m	1e-3
u	1e-6
μ	1e-6
n	1e-9
p	1e-12
f	1e-15
a	1e-18
z	1e-21
y	1e-24

Why not just define constants like `const M=1000000`?

That was considered but it has two downsides

1. Lower accuracy

For example, compare:

julia> @SI 100a
1.0e-16

julia> const a = 1e-18
1.0e-18

julia> 100a
1.0000000000000001e-16

As you can see the 100 * 1e-18 has worse accuracy.

2. Namespace pollution

The other downside of defining constants for the scaling factors is it uses a lot of single character variables. With @SI it reads a block in and only converts expressions with a literal number followed by an SI scaling factor. For example:

julia> function f(k)
          c1 = k + 2k
          c2 = @SI k + 2k
          return (c1=c1, c2=c2)
       end
f (generic function with 1 method)

julia> f(10)
(c1 = 30, c2 = 2010.0)

Note that for c2 the k in 2k was interpreted as 2*1e3 while the preceeding k was not. If const k = 1000 was defined at the top level then the argument k would take precedence and k scalings inside f would not work.

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