Re: [xsl] n-tuple sequences, the constraints they must satisfy, and their XPath expressions
2017-11-23 17:00:46
Conditions 1-3 wouldn't work on their own.
i.e. one could introduce items that do not belong to the original set.
So one additional constraint has to check that.
every $s in $sequences[item] satisfies (
every $item in $s/item satisfies (
some $i in $set satisfies deep-equal($i, $item)))
On top of that the deep-equal uniqueness check for sequences would be
necessary if you drop constraint 4.
every $s in $sequences, $t in ($sequences except $s) satisfies
not(deep-equal($s, $t))
Instead I think Rogers' forth condition is _absolutly marvelous_.
Overall it enforces some kind of induction constraint on the sequences.
"if you have one sequence that isn't full length, there have to be $n
bigger sequences that have been extended with each of the items from the
set"
I would be surprised if it would be necessary to have more than just the
constraints 3 and 4 to decide the combinatorical question. I played
around, but "lengthy" (see below) gave always the same result as
"compressed"
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:math="http://www.w3.org/2005/xpath-functions/math"
exclude-result-prefixes="math">
<xsl:output method="xml" encoding="UTF-8" indent="yes"/>
<xsl:template match="/" >
<xsl:variable name="set">
<item>A</item>
<item>B</item>
</xsl:variable>
<xsl:variable name="sequences">
<sequence />
<sequence>
<item>A</item>
</sequence>
<sequence>
<item>B</item>
</sequence>
<sequence>
<item>A</item>
<item>A</item>
</sequence>
<sequence>
<item>A</item>
<item>B</item>
</sequence>
<sequence>
<item>B</item>
<item>A</item>
</sequence>
<sequence>
<item>B</item>
<item>B</item>
</sequence>
</xsl:variable>
<xsl:variable name="n" select="count($set/item)" />
<evaluation n="{$n}">
<compressed>
<xsl:comment>The total number of sequences is sum(n^k)
for k = 0 to n</xsl:comment>
<constraint no="1">
<xsl:value-of select="count($sequences/sequence) eq
sum(for $k in 0 to $n return math:pow($n, $k))" />
</constraint>
<xsl:comment>Inductional proof</xsl:comment>
<constraint no="2">
<xsl:value-of select="
every $s in $sequences/sequence[count(item) lt $n]
satisfies
every $i in $set/item satisfies
some $sequence-extended in $sequences/sequence
satisfies
deep-equal($sequence-extended/item,
($s/item, $i))" />
</constraint>
</compressed>
<lengthy>
<xsl:comment>sequence[empty(item)]</xsl:comment>
<constraint no="1">
<xsl:value-of select="every $s in
$sequences/sequence satisfies count($s/item) le $n" />
</constraint>
<xsl:comment>All sequences have a length less than or
equal to count($items)</xsl:comment>
<constraint no="2">
<xsl:value-of select="every $s in
$sequences/sequence satisfies count($s/item) le $n" />
</constraint>
<xsl:comment>The total number of sequences is sum(n^k)
for k = 0 to n</xsl:comment>
<constraint no="3">
<xsl:value-of select="count($sequences/sequence) eq
sum(for $k in 0 to $n return math:pow($n, $k))" />
</constraint>
<xsl:comment>All sequences are unique with respect to
item-type and -order</xsl:comment>
<constraint no="4">
<xsl:value-of select="every $s in
$sequences/sequence, $t in ($sequences/sequence except $s) satisfies
not(deep-equal($s, $t))" />
</constraint>
<xsl:comment>All non-empty sequences must only contain
items from the set</xsl:comment>
<constraint no="5">
<xsl:value-of select="
every $s in $sequences/sequence[item] satisfies (
every $item in $s/item satisfies (
some $i in $set/item satisfies
deep-equal($i, $item)
)
)" />
</constraint>
</lengthy>
</evaluation>
</xsl:template>
</xsl:stylesheet>
Best regards
Christoph Naber
Am 22.11.2017 um 20:38 schrieb David Carlisle
d(_dot_)p(_dot_)carlisle(_at_)gmail(_dot_)com:
your condition 4 is the most complicated and I don't think you need > it, given conditions 1-3 you just need to say that no two of your >
sequences are deep-equal. > > David > > On 22 November 2017 at 18:53,
Costello, Roger L. costello(_at_)mitre(_dot_)org >
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote: >> Hi Folks, >> >>
Thank you for your help this past week in answering my question >> about
sequences. Below is a description of the sequences, the >> constraints
they must satisfy, and XPath expressions for >> implementing the
constraints. /Roger >> >> Problem: Sometimes you want all possible
sequences of elements of a >> set with lengths from 0 to n, where n is
the number of elements in >> the set. Such sequences are called
n-tuples, or, permutations with >> repetition. >>
(https://en.wikipedia.org/wiki/Permutation#Permutations_with_repetition)
>> >> >> Let's look at some examples.
>> Here is a set: {A, B} >> >> Here are the valid sequences: (), (A),
(B), (A, A), (A, B), (B, A), >> (B, B) >> >> Notice it has: - The empty
sequence. - Two sequences, one for each >> element in the set. - Four
sequences, each consisting of two >> elements, in all permutations. >>
>> Total number of sequences: 7 >> >> Suppose the set contains three
elements: {A, B, C} >> >> Then here are the valid sequences: >> >> (),
(A), (B), (C), (A, A), (A, B), (A, C), (B, A), (B, B), (B, C), >> (C,
A), (C, B), (C, C), (A, A, A), (A, A, B), (A, A, C), (A, B, A), >> (A,
B, B), (A, B, C), (A, C, A), (A, C, B), (A, C, C), (B, A, A), >> (B, A,
B), (B, A, C), (B, B, A), (B, B, B), (B, B, C), (B, C, A), >> (B, C, B),
(B, C, C), (C, A, A), (C, A, B), (C, A, C), (C, B, A), >> (C, B, B), (C,
B, C), (C, C, A), (C, C, B), (C, C, C) >> >> Notice it has: - The empty
sequence. - Three sequences, one for >> each element in the set. - Nine
sequences, each consisting of two >> elements, in all permutations. -
Twenty-seven sequences, each >> consisting of three elements, in all
permutations. >> >> Total number of sequences: 40 >> >> If the set has 4
elements, then the total number of sequences is >> 341. >> >> The number
of sequences grows rapidly as the number of elements in >> the set
increases. >> >> Of all possible sequences in the universe, only certain
sequences >> are valid (i.e., have the desired properties). What are the
>> constraints that sequences must satisfy to be valid? >> >> Here are
the constraints that sequences must satisfy: >> >> Constraint 1. There
must be an empty sequence. Constraint 2. All >> sequences have a length
less than or equal to n (the length of the >> set). Constraint 3. The
total number of sequences is sum(n^k) for k >> = 0 to n. Constraint 4.
For every sequence s that does not already >> have the maximum length,
there is, for every item i in the set, an >> (extended) sequence s'
whose items are the same as s plus item i. >> >> Let's look at an XML
representation of the sequences and how to >> express the constraints
using XPath. >> >> Here is an XML representation of a set containing two
elements: >> >> <set> <item>A</item> <item>B</item> </set> >> >> Here is
an XML representation of the sequences for that set: >> >> <sequences>
<sequence/> <sequence> <item>A</item> </sequence> >> <sequence>
<item>B</item> </sequence> <sequence> <item>A</item> >> <item>A</item>
</sequence> <sequence> <item>A</item> >> <item>B</item> </sequence>
<sequence> <item>B</item> >> <item>A</item> </sequence> <sequence>
<item>B</item> >> <item>B</item> </sequence> </sequences> >> >> The
empty sequence () is represented by: >> >> <sequence/> >> >> The
sequence (A) is represented by: >> >> <sequence> <item>A</item>
</sequence> >> >> The sequence (A, B) is represented by: >> >>
<sequence> <item>A</item> <item>B</item> </sequence> >> >> And so forth.
>> >> Below are XPath expressions for each of the constraints. >> >>
Note: assume the root element <sequences> is the context node, $set >>
is a variable holding the set XML document, and $n is a variable >>
holding the number of elements in the set. >> >> Constraint 1. There
must be an empty sequence. >> >> sequence[empty(item)] >> >> Constraint
2. All sequences have a length less than or equal to n. >> >> every
$sequence in sequence satisfies count($sequence/item) le $n >> >>
Constraint 3. The total number of sequences is sum(n^k) for k = 0 >> to
n. >> >> count(sequence) = sum(for $i in 0 to $n return math:pow($n,
$i)) >> >> Constraint 4. For every sequence s that does not already have
the >> maximum length, there is, for every item i in the set, an >>
(extended) sequence s' whose items are the same as s plus item i. >> >>
every $sequence in sequence[count(item) lt $n] satisfies every >> $item
in $set//item satisfies some $sequence-extended in sequence >> satisfies
deep-equal($sequence-extended/item, ($sequence/item, >> $item)) >> >>
Acknowledgement >> >> Thank you to the following people for their
fantastic help with >> creating the XPath expressions: >> >> - David
Carlisle - Michael Kay - Christoph Naber >> >
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