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October 25, 2016 06:58
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Dual Number on Elixir
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import Kernel, except: [+: 1, +: 2, -: 1, -: 2, *: 2, /: 2] | |
defprotocol Arithmetic do | |
def left + right | |
def left - right | |
def left * right | |
def left / right | |
def +value | |
def -value | |
end | |
defimpl Arithmetic, for: Integer do | |
def left + right, do: Kernel.+(left , right) | |
def left - right, do: Kernel.-(left , right) | |
def left * right, do: Kernel.*(left , right) | |
def left / right, do: Kernel./(left , right) | |
def +value, do: Kernel.+(value) | |
def -value, do: Kernel.-(value) | |
end | |
defimpl Arithmetic, for: Integer do | |
def left + right, do: Kernel.+(left , right) | |
def left - right, do: Kernel.-(left , right) | |
def left * right, do: Kernel.*(left , right) | |
def left / right, do: Kernel./(left , right) | |
def +value, do: Kernel.+(value) | |
def -value, do: Kernel.-(value) | |
end | |
defmodule DualNumber do | |
import Arithmetic | |
defstruct a: 0, b: 0 | |
def conj(d) do | |
%DualNumber{ a: d.a, b: -d.b} | |
end | |
defimpl Inspect do | |
def inspect(%DualNumber{a: a, b: b}, _opts) do | |
"#{a}+#{b}ε" | |
end | |
end | |
end | |
defimpl Arithmetic, for: DualNumber do | |
def left + right do | |
%DualNumber{ a: Kernel.+(left.a, right.a), | |
b: Kernel.+(left.b, right.b) } | |
end | |
def left - right do | |
%DualNumber{ a: Kernel.-(left.a, right.a), | |
b: Kernel.-(left.b, right.b) } | |
end | |
def left * right do | |
%DualNumber{ a: Kernel.*(left.a, right.a), | |
b: Kernel.+(Kernel.*(left.a, right.b), Kernel.*(left.b, right.a)) } | |
end | |
def left / right do | |
(left * %DualNumber{a: right.a, b: Kernel.-(right.b)}) / %DualNumber{a: Kernel.*(right.a, right.a), b: 0} | |
end | |
def +value, do: value | |
def -value, do: %DualNumber{a: Kernel.-(value.a), b: Kernel.-(value.b)} | |
end | |
defmodule Test do | |
import Arithmetic | |
import DualNumber | |
def f(x) do | |
(%DualNumber{a: 4, b: 0} * x + %DualNumber{a: 3, b: 0}) * x + %DualNumber{a: 2, b: 0} | |
end | |
def df(x) do | |
%DualNumber{a: 8, b: 0} * x + %DualNumber{a: 3, b: 0} | |
end | |
end |
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