Eigenmonzo: Difference between revisions

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A [[regular temperament]] transforms untempered intervals into tempered intervals, which changes most of their sizes. Only a small set of exceptional intervals do not change in size. This set of unchanged intervals depends on the choice of tuning.  
A [[regular temperament]] transforms untempered intervals into tempered intervals, which changes most of their sizes. Only a small set of exceptional intervals do not change in size. This set of unchanged intervals depends on the choice of tuning.  


A popular example of an eigenmonzo is the JI interval {{monzo|0 0 1}}, or 1:5, when it is mapped by [[quarter-comma meantone]]; because this temperament tuning's generator is defined as exactly one-quarter the size of the interval 1:5, it remains justly tuned.
A popular example of an eigenmonzo is the JI interval {{monzo| 0 0 1 }}, or 1:5, when it is mapped by [[quarter-comma meantone]]; because this temperament tuning's generator is defined as exactly one-quarter the size of the interval 1:5, it remains justly tuned.


For any pure-octave temperament tuning, {{monzo|1}}, aka 1:2, is an eigenmonzo.
For any pure-octave temperament tuning, {{monzo| 1 }}, aka 1:2, is an eigenmonzo.


A [[rank]]-n temperament can have up to n different eigenmonzos — one for each [[generator]].
A [[rank]]-''n'' temperament can have up to ''n'' different eigenmonzos — one for each [[generator]].


== With respect to the projection matrix ==
== With respect to the projection matrix ==


The "eigen" part of the term "eigenmonzo" comes from the fact that these intervals are [https://en.wikipedia.org/wiki/Eigenvalues_and_eigenvectors eigenvectors] of the tuning's [[projection matrix]] (not the [[Temperament_mapping_matrices|temperament's mapping matrix]]). Only eigenvectors of the projection matrix with [https://en.wikipedia.org/wiki/Eigenvalues_and_eigenvectors eigenvalue] equal to 1 are considered eigenmonzos, while those with eigenvalue equal to 0 are the vanishing commas of the temperament; in other words, a vector that is a monzo and an eigenvector is not necessarily an eigenmonzo.  
The "eigen" part of the term "eigenmonzo" comes from the fact that these intervals are [[wikipedia: Eigenvalues and eigenvectors|eigenvectors]] of the tuning's [[projection matrix]] (not the [[Temperament_mapping_matrices|temperament's mapping matrix]]). Only eigenvectors of the projection matrix with [[wikipedia: Eigenvalues and eigenvectors|eigenvalue]] equal to 1 are considered eigenmonzos, while those with eigenvalue equal to 0 are the vanishing commas of the temperament; in other words, a vector that is a monzo and an eigenvector is not necessarily an eigenmonzo.  


The "monzo" part of "eigenmonzo" should not be taken to imply that the interval is notated in monzo form, e.g. {{monzo|2 -1}}; for example, 4/3 may be called an eigenmonzo.
The "monzo" part of "eigenmonzo" should not be taken to imply that the interval is notated in monzo form, e.g. {{monzo| 2 -1 }}; for example, 4/3 may be called an eigenmonzo.


== See also ==
== See also ==
* [[Fractional monzo]]: for more mathematical information
* [[Eigenmonzo subgroup]]


* [[fractional monzo]]: for more mathematical information
[[Category:Regular temperament theory]]
* [[eigenmonzo subgroup]]
[[Category:Terms]]