John,
I don't understand how you have identified hh as the
inverse of h. I see that it does accomplish the desired or
simpler result of using { rather that }, but in general how
can an inverse like hh be identified from its dual (is dual
the right terminology)? That is, I thought I could use h
with amend, but if I can always find hh from h and then use
{, that could be superior. Also, could you demonstrate that
h and hh are really inverses. My understanding says that an
inverse reverses the effect of its dual, but I don't see hh
reversing h. Are you saying that { and } are inverse
(functors -- I don't even know what a functor is, but this
sounds like it might be right) and if { and } are
inverses, then that is a revelation to me.
I was pleased to be able to find the } scheme. h is
determined in my application directly, because for example
in this case I can directly observe permutation cycles like
(2 1; 0 1).
I don't really understand what you don't understand.
Are you saying that h is not usually called a permutation
vector, and I am misnaming it?
Thank you very much for your attention to my
musings.
(B=)
On Mon, 10 Jul 2006, John Randall wrote:
+ Brian Schott wrote:
+
+ > More recently I have been creating permutation vectors of a
+ > different sort using "permute" as in the following example inspired by one
+ > in the J vocabulary, called h.
+ >
+ > ]h =: (2 1; 0 1) C. i.4
+ > 1 2 0 3
+ >
+ > But h cannot be used in the "from" form h&{"1 to permute other vectors.
+ > Instead I have found that "amend" in (h})"1~ is effective.
+ >
+ > ]k=: 0 1 2 3,:4 5 6 7
+ > 0 1 2 3
+ > 4 5 6 7
+ > (h})"1~ k
+ > 2 0 1 3
+ > 6 4 5 7
+
+ Could you explain what you are getting at here? The permutation you are
+ using is not h but its inverse
+
+ hh=:2 0 1 3
+
+ and this behaves perfectly normally:
+
+ hh {"1 k
+ 2 0 1 3
+ 6 4 5 7
+
+ Amend works rather than select because of this inversion.
+
+ Best wishes,
+
+ John
+
+
+ ----------------------------------------------------------------------
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+
(B=) <----------my "sig"
Brian Schott
Atlanta, GA, USA
schott DOT bee are eye eh en AT gee em ae eye el DOT com
http://schott.selfip.net/~brian/
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