Re: how to calculate an index and vice versa
- To: mathgroup at smc.vnet.net
- Subject: [mg119288] Re: how to calculate an index and vice versa
- From: Ray Koopman <koopman at sfu.ca>
- Date: Sun, 29 May 2011 07:36:26 -0400 (EDT)
- References: <irqlpg$e9a$1@smc.vnet.net>
On May 28, 4:20 am, ferradini <gianmarco.ferrad... at email.it> wrote: > given n numbers (eg. 1 to 90) > I can build the following list of numbers k (in this case 4) > > 1, 2, 3, 4 associated index -> 0 > 1, 2, 3, 5 associated index -> 1 > 1, 2, 3, 6 associated index -> 2 > 1, 2, 3, 7 associated index -> 3 > 1, 2, 3, 8 ................... .... > 1, 2, 3, 9 ....................... > ....................... > ....................... > 10, 41, 60, 61 associated index -> 954722 > ....................... > ....................... > 87, 88, 89, 90 associated index -> 2555190 > I need to build an algorithm to assign eg 4 elemnti can obtain its index > in the list > (1, 2, 3, 7 return 3) > > The second algorithm is 'inverse: given a number such as 954722 I get > the four elements 87; 88, 89, 90. > The elemnti in the list are always sorted values. > > I thank those who will send me information on the subject to follow > Thank ferradini You want RankKSubset and UnrankKSubset, in Combinatorica.