Thread Subject: Greatest commmon divisor

Hi, any one know how can get the gcd for an array. The function gcd() in matlabe will give result for a array.
for example I want to get 2 for the array A= [10 2 10 -4 2 0];
Is there any function to do that? or how can I do that?

Thanks

"Feng" <nclxin@hotmail.com> wrote in message <ghukju$ksu$1@fred.mathworks.com>...
> Hi, any one know how can get the gcd for an array. The function gcd() in matlabe > will give result for two scalar numbers.
> for example I want to get 2 for the array A= [10 2 10 -4 2 0];
> Is there any function to do that? or how can I do that?
>
> Thanks

"Feng" <nclxin@hotmail.com> wrote in message <ghul2u$rfp$1@fred.mathworks.com>...
> "Feng" <nclxin@hotmail.com> wrote in message <ghukju$ksu$1@fred.mathworks.com>...
> > Hi, any one know how can get the gcd for an array. The function gcd() in matlabe > will give result for two scalar numbers.
> > for example I want to get 2 for the array A= [10 2 10 -4 2 0];
> > Is there any function to do that? or how can I do that?
> >
> > Thanks

  You could always use an old-fashioned for-loop:

c = A(1);
for k = 2:length(A)
 c = gcd(c,A(k));
end

Roger Stafford

In article <ghukju$ksu$1@fred.mathworks.com>, nclxin@hotmail.com says...
> Hi, any one know how can get the gcd for an array. The function gcd() in matlabe will give result for a array.
> for example I want to get 2 for the array A= [10 2 10 -4 2 0];
> Is there any function to do that? or how can I do that?
>
> Thanks
>

Check out the function arrayfun

--
Loren
http://blogs.mathworks.com/loren

Loren Shure <loren@mathworks.com> wrote in message <MPG.23b0d09e505fb8f4989907@news.mathworks.com>...
> >
>
> Check out the function arrayfun
>

I can't see how arrayfun would be used here. I rather stick with Roger's for-loop solution.

Bruno

"Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message <ghum4l$d95$1@fred.mathworks.com>...
> "Feng" <nclxin@hotmail.com> wrote in message <ghul2u$rfp$1@fred.mathworks.com>...
> > "Feng" <nclxin@hotmail.com> wrote in message <ghukju$ksu$1@fred.mathworks.com>...
> > > Hi, any one know how can get the gcd for an array. The function gcd() in matlabe > will give result for two scalar numbers.
> > > for example I want to get 2 for the array A= [10 2 10 -4 2 0];
> > > Is there any function to do that? or how can I do that?
> > >
> > > Thanks
>
> You could always use an old-fashioned for-loop:
>
> c = A(1);
> for k = 2:length(A)
> c = gcd(c,A(k));
> end
>
> Roger Stafford


What about

min(gcd(A(1:end-1),A(2:end)))

Jos

"Jos " <#10584@fileexchange.com> wrote in message <gi7mqt$87b$1@fred.mathworks.com>...
> "Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message <ghum4l$d95$1@fred.mathworks.com>...
> > "Feng" <nclxin@hotmail.com> wrote in message <ghul2u$rfp$1@fred.mathworks.com>...
> > > "Feng" <nclxin@hotmail.com> wrote in message <ghukju$ksu$1@fred.mathworks.com>...
> > > > Hi, any one know how can get the gcd for an array. The function gcd() in matlabe > will give result for two scalar numbers.
> > > > for example I want to get 2 for the array A= [10 2 10 -4 2 0];
> > > > Is there any function to do that? or how can I do that?
> > > >
> > > > Thanks
> >
> > You could always use an old-fashioned for-loop:
> >
> > c = A(1);
> > for k = 2:length(A)
> > c = gcd(c,A(k));
> > end
> >
> > Roger Stafford
>
>
> What about
>
> min(gcd(A(1:end-1),A(2:end)))
>
> Jos

On second thoughts, you have to remove the zeros first, otherwise something like
A = [x 0 0 y]
will always give 0, instead of gcd(x,y)

Jos

>
> min(gcd(A(1:end-1),A(2:end)))
>

Jos, this does not work

A=[15 30 20]

gcd is 5, not 10

Bruno

"Jos " <#10584@fileexchange.com> wrote in message <gi7mqt$87b$1@fred.mathworks.com>...
> What about
>
> min(gcd(A(1:end-1),A(2:end)))
>
> Jos

  I don't think that would work, Jos, even with zeros eliminated. Let A = [15,21,35]. Then gcd(A(1:end-1),A(2:end)) would yield [3,7] but the minimum of these is not the gcd of the three combined quantities. The greatest common factor of all three is simply 1, not this minimum.

Roger Stafford

"Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message <gi7o45$297$1@fred.mathworks.com>...
> "Jos " <#10584@fileexchange.com> wrote in message <gi7mqt$87b$1@fred.mathworks.com>...
> > What about
> >
> > min(gcd(A(1:end-1),A(2:end)))
> >
> > Jos
>
> I don't think that would work, Jos, even with zeros eliminated. Let A = [15,21,35]. Then gcd(A(1:end-1),A(2:end)) would yield [3,7] but the minimum of these is not the gcd of the three combined quantities. The greatest common factor of all three is simply 1, not this minimum.
>
> Roger Stafford

Yep, you and Bruno are right, of course. I was just wondering why Loren suggested arrayfun, and so I was looking for a function that could do this.

Jos

In article <gi7uei$22l$1@fred.mathworks.com>, #10584@fileexchange.com
says...
> "Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message <gi7o45$297$1@fred.mathworks.com>...
> > "Jos " <#10584@fileexchange.com> wrote in message <gi7mqt$87b$1@fred.mathworks.com>...
> > > What about
> > >
> > > min(gcd(A(1:end-1),A(2:end)))
> > >
> > > Jos
> >
> > I don't think that would work, Jos, even with zeros eliminated. Let A = [15,21,35]. Then gcd(A(1:end-1),A(2:end)) would yield [3,7] but the minimum of these is not the gcd of the three combined quantities. The greatest common factor of all three is simply 1, not this minimum.
> >
> > Roger Stafford
>
> Yep, you and Bruno are right, of course. I was just wondering why Loren suggested arrayfun, and so I was looking for a function that could do this.
>
> Jos
>
>

Perhaps I misread the problem. I thought the OP wanted GCD of each
"pair" of points in 2 arrays. Probably read too fast...

--
Loren
http://blogs.mathworks.com/loren