finding all factors of a number question
in [Matlab]
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From: M Mouse on 25 Aug 2005 14:18 hey, I know this is a general math problem, but I was wondering if there was a spiffy matlab way of doing it... say I have a number X and I want to find three other numbers (a, b, c) such that when they are multiplied together they equal X. a*b*c=X I want to generate a list of all possibilities of a, b, and c for a given X. Is there an easy way to change this to find four (or five or six) numbers? I know this problem is a general 'finding primes' type of question, but in my case all my values for X are 'small' (less than 500)... Thanks in advance...
From: Jos on 25 Aug 2005 14:46 M Mouse wrote: > > > hey, > I know this is a general math problem, but I was wondering if there > was a spiffy matlab way of doing it... > say I have a number X and I want to find three other numbers (a, b, > c) such that when they are multiplied together they equal X. > a*b*c=X > I want to generate a list of all possibilities of a, b, and c for a > given X. > Is there an easy way to change this to find four (or five or six) > numbers? > I know this problem is a general 'finding primes' type of question, > but in my case all my values for X are 'small' (less than 500)... > Thanks in advance... Let N be your number and M the number of "factors"". Then: p = perms(factor(N)) ; if length(p) >= M, y = unique([p(:,1:M-1) prod(p(:,M:end),2)],'rows') ; else error('No solution') end will do the job. hth Jos
From: Paul Skoczylas on 25 Aug 2005 15:03 "M Mouse" <minnieM(a)mailinator.com> wrote in message news:ef121e5.-1(a)webx.raydaftYaTP... > hey, > I know this is a general math problem, but I was wondering if there > was a spiffy matlab way of doing it... > say I have a number X and I want to find three other numbers (a, b, > c) such that when they are multiplied together they equal X. > a*b*c=X > I want to generate a list of all possibilities of a, b, and c for a > given X. > Is there an easy way to change this to find four (or five or six) > numbers? > I know this problem is a general 'finding primes' type of question, > but in my case all my values for X are 'small' (less than 500)... > Thanks in advance... "factor" will find all the prime factors of a number. That's somewhere for you to start, anyway... -Paul
From: Jos on 25 Aug 2005 15:27 Jos wrote: > > > M Mouse wrote: >> >> >> hey, >> I know this is a general math problem, but I was wondering if > there >> was a spiffy matlab way of doing it... >> say I have a number X and I want to find three other numbers (a, > b, >> c) such that when they are multiplied together they equal X. >> a*b*c=X >> I want to generate a list of all possibilities of a, b, and c for > a >> given X. >> Is there an easy way to change this to find four (or five or six) >> numbers? >> I know this problem is a general 'finding primes' type of > question, >> but in my case all my values for X are 'small' (less than 500)... >> Thanks in advance... > > Let N be your number and M the number of "factors"". > > Then: > > p = perms(factor(N)) ; > if length(p) >= M, > y = unique([p(:,1:M-1) prod(p(:,M:end),2)],'rows') ; > else > error('No solution') > end > > will do the job. > > hth > Jos A sort was missing to eliminate duplicates: p = perms(factor(N)) ; if length(p) >= M, y = unique(sort([p(:,1:M-1) prod(p(:,M:end),2)],2),'rows') ; else error('No solution') end Jos
From: Jos on 25 Aug 2005 16:35
Jos wrote: > > > Jos wrote: >> >> >> M Mouse wrote: >>> >>> >>> hey, >>> I know this is a general math problem, but I was wondering if >> there >>> was a spiffy matlab way of doing it... >>> say I have a number X and I want to find three other numbers > (a, >> b, >>> c) such that when they are multiplied together they equal X. >>> a*b*c=X >>> I want to generate a list of all possibilities of a, b, and c > for >> a >>> given X. >>> Is there an easy way to change this to find four (or five or > six) >>> numbers? >>> I know this problem is a general 'finding primes' type of >> question, >>> but in my case all my values for X are 'small' (less than > 500)... >>> Thanks in advance... >> >> Let N be your number and M the number of "factors"". >> >> Then: >> >> p = perms(factor(N)) ; >> if length(p) >= M, >> y = unique([p(:,1:M-1) prod(p(:,M:end),2)],'rows') ; >> else >> error('No solution') >> end >> >> will do the job. >> >> hth >> Jos > > A sort was missing to eliminate duplicates: > > p = perms(factor(N)) ; > if length(p) >= M, > y = unique(sort([p(:,1:M-1) prod(p(:,M:end),2)],2),'rows') ; > else > error('No solution') > end > > Jos ahum ... on testing this function it fails in some occasions, e.g. when N=32 and M=3 ... Jos |