Comma basis: Difference between revisions

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This is a basic introduction to this concept. For a more mathematical take, see [[dual list]].

A '''comma basis''' is a [[basis]] for the [[wikipedia: Kernel (linear algebra)|nullspace]] (sometimes also called the "kernel") of a [[regular temperament|temperament]]. It consists of <math>n</math> [[wikipedia: Linear independence|linearly independent]] vectors, where <math>n</math> is the [[nullity]], each one representing a [[comma]] that is [[~~tempered out~~]].

A '''comma basis''' is a [[basis]] for the [[wikipedia: Kernel (linear algebra)|nullspace]] (sometimes also called the "kernel") of a [[regular temperament|temperament]]. It consists of <math>n</math> [[wikipedia: Linear independence|linearly independent]] vectors, where <math>n</math> is the [[nullity]], each one representing a [[comma]] that is made to [[vanish]].

Linear independence means that no comma can be found as the sum of any multiples of the other commas. For example, consider the set of three commas 81/80, 126/125, and 225/224. As vectors those are {{vector|-4 4 -1 0}}, {{vector|1 2 -3 1}}, and {{vector|-5 2 2 -1}}. Notice that the third comma is actually the difference between the other two; {{vector|-4 4 -1 0}} - {{vector|1 2 -3 1}} = {{vector|-5 2 2 -1}}, or as cents, 21.51¢ - 13.80¢ = 7.71¢. So, if two of these three commas are ever ~~tempered out~~ (mapped to 0¢), then the third one necessarily is also ~~tempered out~~. Therefore, we only need to pick two of these commas to put in our comma basis; the third one would be implied.

Linear independence means that no comma can be found as the sum of any multiples of the other commas. For example, consider the set of three commas 81/80, 126/125, and 225/224. As vectors those are {{vector|-4 4 -1 0}}, {{vector|1 2 -3 1}}, and {{vector|-5 2 2 -1}}. Notice that the third comma is actually the difference between the other two; {{vector|-4 4 -1 0}} - {{vector|1 2 -3 1}} = {{vector|-5 2 2 -1}}, or as cents, 21.51¢ - 13.80¢ = 7.71¢. So, if two of these three commas are ever made to vanish (mapped to 0¢), then the third one necessarily is also made to vanish. Therefore, we only need to pick two of these commas to put in our comma basis; the third one would be implied.

The comma basis can be thought of either as a list of vectors or as a matrix formed by putting these vectors (as columns) together. Besides, it is often presented in terms of ratios for convenience. Various [[Normal lists #Normal interval lists|normal forms]] have been developed as identifiers of temperaments.

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 This is a basic introduction to this concept. For a more mathematical take, see [[dual list]].
-A '''comma basis''' is a [[basis]] for the [[wikipedia: Kernel (linear algebra)|nullspace]] (sometimes also called the "kernel") of a [[regular temperament|temperament]]. It consists of <math>n</math> [[wikipedia: Linear independence|linearly independent]] vectors, where <math>n</math> is the [[nullity]], each one representing a [[comma]] that is [[tempered out]].
+A '''comma basis''' is a [[basis]] for the [[wikipedia: Kernel (linear algebra)|nullspace]] (sometimes also called the "kernel") of a [[regular temperament|temperament]]. It consists of <math>n</math> [[wikipedia: Linear independence|linearly independent]] vectors, where <math>n</math> is the [[nullity]], each one representing a [[comma]] that is made to [[vanish]].
-Linear independence means that no comma can be found as the sum of any multiples of the other commas. For example, consider the set of three commas 81/80, 126/125, and 225/224. As vectors those are {{vector|-4 4 -1 0}}, {{vector|1 2 -3 1}}, and {{vector|-5 2 2 -1}}. Notice that the third comma is actually the difference between the other two; {{vector|-4 4 -1 0}} - {{vector|1 2 -3 1}} = {{vector|-5 2 2 -1}}, or as cents, 21.51¢ - 13.80¢ = 7.71¢. So, if two of these three commas are ever tempered out (mapped to 0¢), then the third one necessarily is also tempered out. Therefore, we only need to pick two of these commas to put in our comma basis; the third one would be implied.
+Linear independence means that no comma can be found as the sum of any multiples of the other commas. For example, consider the set of three commas 81/80, 126/125, and 225/224. As vectors those are {{vector|-4 4 -1 0}}, {{vector|1 2 -3 1}}, and {{vector|-5 2 2 -1}}. Notice that the third comma is actually the difference between the other two; {{vector|-4 4 -1 0}} - {{vector|1 2 -3 1}} = {{vector|-5 2 2 -1}}, or as cents, 21.51¢ - 13.80¢ = 7.71¢. So, if two of these three commas are ever made to vanish (mapped to 0¢), then the third one necessarily is also made to vanish. Therefore, we only need to pick two of these commas to put in our comma basis; the third one would be implied.
 The comma basis can be thought of either as a list of vectors or as a matrix formed by putting these vectors (as columns) together. Besides, it is often presented in terms of ratios for convenience. Various [[Normal lists #Normal interval lists|normal forms]] have been developed as identifiers of temperaments.