Module:ET

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This module depends on the following other modules:

This module provides helper functions for equal-step tunings.

Functions

new: Returns an array consisting of the components of an equal-step tuning.

parse: Designed to convert strings in the format [number of steps]ed[equave] into an ET structure, and returns it via the new function. For example, ET.parse("12edo") returns an array containing {12, 2, "edo"}

as_string: Returns the string representation for an ET structure.

backslash_ratio: Converts steps to a proper ratio as a floating-point number.

backslash_display: Displays an ET structure in backslash form ([steps]\[number of divisions]).

cents: Converts the interval an ET structure represents to cents.

hekts: Converts the interval an ET structure represents to hekts (relative cent of 13edt).

approximate: Returns the floor, round, or ceiling of a particular ratio.

tempers_out: Determines if an ET tempers out a provided rational number.

is_highly_composite: Determines if an ET is highly composite.

is_zeta: Determines if an ET holds any zeta records.

why_zeta: Describes what specific properties an ET has if it is a zeta record ET.

local rat = require('Module:Rational')
local seq = require('Module:Sequence')
local p = {}

local common_suffix = {
	['3/2'] = 'f',
	['2'] = 'o',
	['2/1'] = 'o',
	['3'] = 't',
	['3/1'] = 't',
}
local common_ratio = {
	['f'] = rat.new(3, 2),
	['o'] = 2,
	['t'] = 3
}

-- create a ET structure <size>ed<equave>
function p.new(size, equave, suffix)
	size = size or 12
	equave = equave or 2
	if suffix == nil then
		local equave_n, equave_m = rat.as_pair(equave)
		local equave_ratio = rat.as_ratio(equave)
		equave_ratio = equave_ratio:lower()
		suffix = size .. 'ed'
		if common_suffix[equave_ratio] then
			suffix = suffix .. common_suffix[equave_ratio]
		elseif equave_m == 1 then
			suffix = suffix .. equave_n
		else
			suffix = suffix .. equave_ratio
		end
	end
	return { size = size, equave = equave, suffix = suffix }
end

-- parse a ET structure
function p.parse(unparsed)
	local size, suffix, equave = unparsed:match('^(%d+)([Ee][Dd](.+))$')
	if equave == nil then
		return nil
	end
	suffix = suffix:lower()
	size = tonumber(size)
	equave = common_ratio[equave] or rat.parse(equave)
	if size == nil or equave == nil then
		return nil
	end
	return p.new(size, equave, suffix)
end

-- construct a string representation for a ET structure
function p.as_string(et)
	return et.size .. et.suffix
end

-- convert steps to a proper ratio (except that it is a float approximation)
function p.backslash_ratio(et, steps)
	if et.size == 0 then
		return 1
	end
	return rat.as_float(et.equave) ^ (steps / et.size)
end

-- convert steps to cents
function p.cents(et, steps)
	if et.size == 0 then
		return 0
	end
	steps = steps or 1
	return 1200 * steps / et.size * math.log(rat.as_float(et.equave)) / math.log(2)
end

-- convert ratio to steps
-- ratio is a float!
-- towards is one of: -1 (floor), 0 (nearest), 1 (ceil)
function p.approximate(et, ratio, towards)
	towards = towards or 0
	if et.size == 0 then
		return 0
	end
	local exact = math.log(ratio) / math.log(rat.as_float(et.equave)) * et.size
	if towards < 0 then
		return math.floor(exact)
	elseif towards > 0 then
		return math.ceil(exact)
	else
		return math.floor(exact + 0.5)
	end
end

-- determine whether ET is highly composite
function p.is_highly_composite(et)
	et.highly_composite = et.highly_composite or rat.is_highly_composite(et.size)
	return et.highly_composite
end

-- determine whether ET's size could be within one of zeta function-related sequences
function p.is_zeta(et)
	return seq.contains(seq.zeta_peak, et.size) ~= false
		or seq.contains(seq.integral_zeta, et.size) ~= false
		or seq.contains(seq.zeta_gap, et.size) ~= false
end

-- describe why
function p.why_zeta(et, debug_mode)
	local zeta_peak = seq.contains(seq.zeta_peak, et.size)
	local integral_zeta = seq.contains(seq.integral_zeta, et.size)
	local zeta_gap = seq.contains(seq.zeta_gap, et.size)
	
	local markers = {}
	if zeta_peak then
		table.insert(markers, '[[The Riemann zeta function and tuning#Peak EDOs|zeta peak]]')
	elseif zeta_peak == nil then
		table.insert(markers, '[[The Riemann zeta function and tuning#Peak EDOs|zeta peak?]]')
	end
	if integral_zeta then
		table.insert(markers, '[[The Riemann zeta function and tuning#Integral of Zeta EDOs|integral of zeta]]')
	elseif integral_zeta == nil then
		table.insert(markers, '[[The Riemann zeta function and tuning#Integral of Zeta EDOs|integral of zeta?]]')
	end
	if zeta_gap then
		table.insert(markers, '[[The Riemann zeta function and tuning#Zeta Gap EDOs|zeta gap]]')
	elseif zeta_gap == nil then
		table.insert(markers, '[[The Riemann zeta function and tuning#Zeta Gap EDOs|zeta gap?]]')
	end
	return table.concat(markers, ', ')
end

return p