NchooseK
in [Matlab]
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From: Frank Sabouri on 9 Mar 2010 18:51 Hello - I have problem of memory when I run: NK=nchoosek (1:N,K), in which N is >40. I need to generate a "NK", wherein "N" is 140. Does anyone know how I could deal with this problem?! Thanks, Farnk
From: John D'Errico on 9 Mar 2010 19:07 "Frank Sabouri" <Frank.Sabouri(a)gmail.com> wrote in message <hn6mt9$9kb$1(a)fred.mathworks.com>... > Hello - > > I have problem of memory when I run: NK=nchoosek (1:N,K), in which N is >40. I need to generate a "NK", wherein "N" is 140. Does anyone know how I could deal with this problem?! > Rather than just blindly trying to do something, THINK first. How many combinations are you hoping to generate? Just for kicks, try this: nchoosek(140,70) Warning: Result may not be exact. Coefficient is greater than 1.000000e+15 and is only accurate to 15 digits > In nchoosek at 66 ans = 9.3821e+40 Let me see. 10^41 different combinations, suggests you will need on the order of multiple tredecillion bytes of memory. Do you really have that big of a computer? In fact, the number of atoms in the entire Earth is roughly that large. http://pages.prodigy.net/jhonig/bignum/qaearth.html The way to deal with your problem is to make your problems SMALLER. Your computer is not infinitely large or infinitely fast. John
From: Frank Sabouri on 9 Mar 2010 19:42 Hello - Let me ask my question in other way: I have a matrix of data (140X15), I want to randomly generate as much as possible sub-matrices (6X15). It was why I used "nchoosek" to randomly set the sub-matices. There is any function that allow me to creat these submatices. Frank "John D'Errico" <woodchips(a)rochester.rr.com> wrote in message <hn6nra$8rc$1(a)fred.mathworks.com>... > "Frank Sabouri" <Frank.Sabouri(a)gmail.com> wrote in message <hn6mt9$9kb$1(a)fred.mathworks.com>... > > Hello - > > > > I have problem of memory when I run: NK=nchoosek (1:N,K), in which N is >40. I need to generate a "NK", wherein "N" is 140. Does anyone know how I could deal with this problem?! > > > > Rather than just blindly trying to do something, THINK > first. How many combinations are you hoping to > generate? Just for kicks, try this: > > nchoosek(140,70) > Warning: Result may not be exact. Coefficient is greater than 1.000000e+15 and is only accurate to 15 digits > > In nchoosek at 66 > ans = > 9.3821e+40 > > Let me see. 10^41 different combinations, suggests > you will need on the order of multiple tredecillion bytes > of memory. Do you really have that big of a computer? > In fact, the number of atoms in the entire Earth is > roughly that large. > > http://pages.prodigy.net/jhonig/bignum/qaearth.html > > The way to deal with your problem is to make your > problems SMALLER. Your computer is not infinitely > large or infinitely fast. > > John
From: Walter Roberson on 9 Mar 2010 19:40 Frank Sabouri wrote: > Hello - > > I have problem of memory when I run: NK=nchoosek (1:N,K), in which N is > >40. I need to generate a "NK", wherein "N" is 140. Does anyone know > how I could deal with this problem?! What is your K? With N = 140, K = 4 requires about 116 Mb, and K = 5 requires over 3 Gb. K = 10 requires about 4 petabytes (that's the unit above terabytes).
From: Oleg Komarov on 9 Mar 2010 20:00 Walter Roberson <roberson(a)hushmail.com> wrote in message <hn6qam$sv7$1(a)canopus.cc.umanitoba.ca>... > Frank Sabouri wrote: > > Hello - > > > > I have problem of memory when I run: NK=nchoosek (1:N,K), in which N is > > >40. I need to generate a "NK", wherein "N" is 140. Does anyone know > > how I could deal with this problem?! > > What is your K? With N = 140, K = 4 requires about 116 Mb, and K = 5 requires > over 3 Gb. K = 10 requires about 4 petabytes (that's the unit above terabytes). I'm sure only Paris Hilton has a petabyte :| ! Oleg
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