Ringer scale: Difference between revisions

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The [[17-limit]] [[val]] that confirms this scale is CS is {{val|9 15 22 26 32 34 38}}, which written as [[wart]]s is 9bccdefgg. (Note that in this case, where there is two warts this corresponds to the patent val mapping for the prime already being sharp and being warted to be a step sharper. If we assume that every wart means "sharpen by one step from patent val" this val can be written rather curiously as 9bcdefg, which shows that this val is the one sharpening every applicable prime by one step above the [[patent val]] mapping.) One can confirm that the above is CS because if one traverses it step by step, every one-step interval is mapped to one EDOstep which by [[wikipedia:linearity|linearity]] (more precisely, [[epimorphic]]ity) [[#Proof of CS of by linearity|implies CS]]. Note that it is important to preserve the order of these intervals. 14:16 = 16/14 = 8/7 is mapped to one positive step, as is 16:15 = 15/16, as is 15:17 = 17/15. Similarly (or thus/by linearity), 14:15 = 15/14 is mapped to 2 steps, as is 16:17 = 17/16, as is 15:18 = 18/15 = 6/5.

== ~~Proof of~~ CS by ~~linearity of the epimorphic val~~ ==

== Proving CS by hand ==

Because the CS property means that every occurrence of an interval must occur with the same number of steps, it suffices to show that every one-step interval is mapped to one step by the [[val]] that the Ringer scale is constructed with. (This val shows that the Ringer scale is [[epimorphic]].)

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However, conversely, a scale being CS does not imply that such a val exists! In almost all observed practical cases if a scale is CS there is some val, but it is possible to construct scales where, for example, one 1-scalestep interval is equal to the product of more than one other 1-scalestep intervals; that is, if we have 1-scalestep intervals {''a'', ''b'', ''c'', ...} then we can choose ''ab'' as a 1-scalestep interval as long as ''ab'' doesn't occur as a 2-scalestep interval anywhere in the scale, which is why at least one extra 1-scalestep interval ''c'' is necessary to separate instances of ''a'' and ''b''. You can even choose ''b'' = ''a'' but you need to be careful to avoid CS-violating contradictions. For a concrete example, you can use {[[5/4]], [[9/8]], [[45/32]], ...} as 1-scalestep intervals to generate a nonlinear CS scale as long as [[45/32]] does not occur as a 2-scalestep interval anywhere in your scale.

~~=== Sketch of the proof ===~~

~~Consider an ''N''-note [[periodic scale]] with period ''P'' as being defined by a function <math>f: \mathbb{Z} \to \mathbb{Q}_{>0}</math> with <math>f(Nk) = P^k.</math>~~

By the construction of a ringer scale, we are given some [[val]] [[map]] <math>m : \mathbb{Q}_{>0} \to \mathbb{Z}</math> that satisfies <math>m(f(k+1)/f(k)) = 1</math> for all ''k'' in '''Z'''. (This can be checked by hand or by computer as we only need to check one period <i>P</i>'s worth of 1-scalestep intervals.)

By induction this implies <math>m(f(k+s)/f(k)) = s</math> because the intervals from ''k'' to ''k''+1, from ''k''+1 to ''k''+2, ..., from ''k''+''s''-1 to ''k''+''s'' all multiply together. This also implies <math>m(f(k))=k,</math> proving ''f'' to be [[epimorphic]], therefore CS (see proof in the article [[epimorphic scale]]). {{qed}}

== Ringer scales ==

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 The [[17-limit]] [[val]] that confirms this scale is CS is  {{val|9 15 22 26 32 34 38}}, which written as [[wart]]s is 9bccdefgg. (Note that in this case, where there is two warts this corresponds to the patent val mapping for the prime already being sharp and being warted to be a step sharper. If we assume that every wart means "sharpen by one step from patent val" this val can be written rather curiously as 9bcdefg, which shows that this val is the one sharpening every applicable prime by one step above the [[patent val]] mapping.) One can confirm that the above is CS because if one traverses it step by step, every one-step interval is mapped to one EDOstep which by [[wikipedia:linearity|linearity]] (more precisely, [[epimorphic]]ity) [[#Proof of CS of by linearity|implies CS]]. Note that it is important to preserve the order of these intervals. 14:16 = 16/14 = 8/7 is mapped to one positive step, as is 16:15 = 15/16, as is 15:17 = 17/15. Similarly (or thus/by linearity), 14:15 = 15/14 is mapped to 2 steps, as is 16:17 = 17/16, as is 15:18 = 18/15 = 6/5.
-== Proof of CS by linearity of the epimorphic val ==
+== Proving CS by hand ==
 Because the CS property means that every occurrence of an interval must occur with the same number of steps, it suffices to show that every one-step interval is mapped to one step by the [[val]] that the Ringer scale is constructed with. (This val shows that the Ringer scale is [[epimorphic]].)
@@ Line 64: / Line 64: @@
 However, conversely, a scale being CS does not imply that such a val exists! In almost all observed practical cases if a scale is CS there is some val, but it is possible to construct scales where, for example, one 1-scalestep interval is equal to the product of more than one other 1-scalestep intervals; that is, if we have 1-scalestep intervals {''a'', ''b'', ''c'', ...} then we can choose ''ab'' as a 1-scalestep interval as long as ''ab'' doesn't occur as a 2-scalestep interval anywhere in the scale, which is why at least one extra 1-scalestep interval ''c'' is necessary to separate instances of ''a'' and ''b''. You can even choose ''b'' = ''a'' but you need to be careful to avoid CS-violating contradictions. For a concrete example, you can use {[[5/4]], [[9/8]], [[45/32]], ...} as 1-scalestep intervals to generate a nonlinear CS scale as long as [[45/32]] does not occur as a 2-scalestep interval anywhere in your scale.
-=== Sketch of the proof ===
-Consider an ''N''-note [[periodic scale]] with period ''P'' as being defined by a function <math>f: \mathbb{Z} \to \mathbb{Q}_{>0}</math> with <math>f(Nk) = P^k.</math>
-By the construction of a ringer scale, we are given some [[val]] [[map]] <math>m : \mathbb{Q}_{>0} \to \mathbb{Z}</math> that satisfies <math>m(f(k+1)/f(k)) = 1</math> for all ''k'' in '''Z'''. (This can be checked by hand or by computer as we only need to check one period <i>P</i>'s worth of 1-scalestep intervals.)
-By induction this implies <math>m(f(k+s)/f(k)) = s</math> because the intervals from ''k'' to ''k''+1, from ''k''+1 to ''k''+2, ..., from ''k''+''s''-1 to ''k''+''s'' all multiply together. This also implies <math>m(f(k))=k,</math> proving ''f'' to be [[epimorphic]], therefore CS (see proof in the article [[epimorphic scale]]). {{qed}}
 == Ringer scales ==