Combination product set
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Original Wikitext content:
A **combination product set** is a [[scale]] generated by the following means: # A set S of n positive real numbers is the starting point. # All the combinations of k elements of the set are obtained, and their products taken. # These are combined into a set, and then all of the elements of that set are divided by one of them (which one is arbitrary; if a canonical choice is required the smallest element could be used). # The resulting elements are reduced to an octave and sorted in ascending order, resulting in an octave period of a [[periodic scale]] (the usual sort of scale, in other words) which we may call Cps(S, k). This is sometimes called a k)n cps. There are special names for special cases: a 2)4 cps is called a [[hexany]]; both 2)5 and 3)5 cps are called [[dekanies]]; both 2)6 and 4)6 cps are called [[pentadekanies]], and a 3)6 cps an [[eikosany]]. These are normally considered in connection with just intonation, so that the starting set is a set of positive rational numbers, but nothing prevents consideration of the more general case. The idea can be further generalized so that the thing we start from is not a set but a [[http://en.wikipedia.org/wiki/Multiset|multiset]]. A multiset is like a set, but the elements have multiplicites; there can be two, three or any number of a given kind of element. Submultisets of a multiset are also multisets, and the product over a multiset takes account of multiplicity. Hence the 2)4 hexany resulting from the multiset [1,1,3,5] first generates the two-element submultisets, which are [1, 1], [1, 3], [1, 5], [3, 5], and we obtain products 1, 3, 5, and 15. Reducing to an octave gives 5/4, 3/2, 15/8, 2 which can be transposed to 5/4, 4/3, 5/3, 2. In spite of being called a hexany it has only four notes. Cps are closely related to [[Euler genera]], since if we combine 0)n, 1)n, 2)n ... n)n before reducing to an octave, and then reduce, we get an Euler genus.
Original HTML content:
<html><head><title>Combination product sets</title></head><body>A <strong>combination product set</strong> is a <a class="wiki_link" href="/scale">scale</a> generated by the following means:<br /> <br /> <ol><li>A set S of n positive real numbers is the starting point.</li><li>All the combinations of k elements of the set are obtained, and their products taken.</li><li>These are combined into a set, and then all of the elements of that set are divided by one of them (which one is arbitrary; if a canonical choice is required the smallest element could be used).</li><li>The resulting elements are reduced to an octave and sorted in ascending order, resulting in an octave period of a <a class="wiki_link" href="/periodic%20scale">periodic scale</a> (the usual sort of scale, in other words) which we may call Cps(S, k).</li></ol><br /> This is sometimes called a k)n cps. There are special names for special cases: a 2)4 cps is called a <a class="wiki_link" href="/hexany">hexany</a>; both 2)5 and 3)5 cps are called <a class="wiki_link" href="/dekanies">dekanies</a>; both 2)6 and 4)6 cps are called <a class="wiki_link" href="/pentadekanies">pentadekanies</a>, and a 3)6 cps an <a class="wiki_link" href="/eikosany">eikosany</a>. These are normally considered in connection with just intonation, so that the starting set is a set of positive rational numbers, but nothing prevents consideration of the more general case.<br /> <br /> The idea can be further generalized so that the thing we start from is not a set but a <a class="wiki_link_ext" href="http://en.wikipedia.org/wiki/Multiset" rel="nofollow">multiset</a>. A multiset is like a set, but the elements have multiplicites; there can be two, three or any number of a given kind of element. Submultisets of a multiset are also multisets, and the product over a multiset takes account of multiplicity. Hence the 2)4 hexany resulting from the multiset [1,1,3,5] first generates the two-element submultisets, which are [1, 1], [1, 3], [1, 5], [3, 5], and we obtain products 1, 3, 5, and 15. Reducing to an octave gives 5/4, 3/2, 15/8, 2 which can be transposed to 5/4, 4/3, 5/3, 2. In spite of being called a hexany it has only four notes.<br /> <br /> Cps are closely related to <a class="wiki_link" href="/Euler%20genera">Euler genera</a>, since if we combine 0)n, 1)n, 2)n ... n)n before reducing to an octave, and then reduce, we get an Euler genus.</body></html>