I'm trying to find the roots of 100 random polynomials of degree 5 and I need help with finding the roots. I know that I can gernerate 100 polynomials by using
                                          >> x=rand([100 6])
I know that I can't do 
                                          >> roots(x)
because the the input must be a vector. Is there anyway to to find all the roots of 100 random polynomials without generating each polynomial one by one. 

Mark wrote:
> I'm trying to find the roots of 100 random polynomials of degree 5 and I 
> need help with finding the roots. I know that I can gernerate 100 
> polynomials by using
>                                          >> x=rand([100 6])
> I know that I can't do                                          >> roots(x)
> because the the input must be a vector. Is there anyway to to find all 
> the roots of 100 random polynomials without generating each polynomial 
> one by one.

Not for degree 5. For degree 4, there would be exact solutions you could 
plug the coefficients into, but for degree 5 unless you are lucky enough 
to be able to factorize, you need to use something like a binary search 
for sign changes over a hypothesized interval.

I'm not saying that it would not be possible to build a routine that did 
this kind of search in parallel, but it isn't the way the built-in 
routines are set up.

"Mark " <bobbb909@yahoo.com> wrote in message 
news:hrcsta$g22$1@fred.mathworks.com...
> I'm trying to find the roots of 100 random polynomials of degree 5 and I 
> need help with finding the roots. I know that I can gernerate 100 
> polynomials by using
>                                          >> x=rand([100 6])
> I know that I can't do >> roots(x)
> because the the input must be a vector. Is there anyway to to find all the 
> roots of 100 random polynomials without generating each polynomial one by 
> one.

Loop over the rows of x and call ROOTS on each row, storing the roots back 
into rows or columns of another matrix or into a cell array (depending on 
how you need them.)

-- 
Steve Lord
slord@mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ 

"Mark " <bobbb909@yahoo.com> wrote in message <hrcsta$g22$1@fred.mathworks.com>...
> I'm trying to find the roots of 100 random polynomials of degree 5 and I need help with finding the roots. I know that I can gernerate 100 polynomials by using
>                                           >> x=rand([100 6])
> I know that I can't do 
>                                           >> roots(x)
> because the the input must be a vector. Is there anyway to to find all the roots of 100 random polynomials without generating each polynomial one by one. 

a hint:

     help num2cell;
     help cellfun;

us

"Steven Lord" <slord@mathworks.com> wrote in message <hrcuhl$1r6$1@fred.mathworks.com>...
> 
> "Mark " <bobbb909@yahoo.com> wrote in message 
> news:hrcsta$g22$1@fred.mathworks.com...
> > I'm trying to find the roots of 100 random polynomials of degree 5 and I 
> > need help with finding the roots. I know that I can gernerate 100 
> > polynomials by using
> >                                          >> x=rand([100 6])
> > I know that I can't do >> roots(x)
> > because the the input must be a vector. Is there anyway to to find all the 
> > roots of 100 random polynomials without generating each polynomial one by 
> > one.
> 
> Loop over the rows of x and call ROOTS on each row, storing the roots back 
> into rows or columns of another matrix or into a cell array (depending on 
> how you need them.)
> 
> -- 
> Steve Lord
> slord@mathworks.com
> comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ 
> 
How would I wrtie the for loop? Here is what I got so far

N=100;
x=zeros(100, 6);    % cretes an empty 100 x 6 matrix

for k=1:N
    x(k)=roots(rand([1 6]));
end

x
I know that this won't work so how can I get it to work.

"Mark " <bobbb909@yahoo.com> wrote in message <hri8s0$gjm$1@fred.mathworks.com>...
> "Steven Lord" <slord@mathworks.com> wrote in message <hrcuhl$1r6$1@fred.mathworks.com>...
> > 
> > "Mark " <bobbb909@yahoo.com> wrote in message 
> > news:hrcsta$g22$1@fred.mathworks.com...
> > > I'm trying to find the roots of 100 random polynomials of degree 5 and I 
> > > need help with finding the roots. I know that I can gernerate 100 
> > > polynomials by using
> > >                                          >> x=rand([100 6])
> > > I know that I can't do >> roots(x)
> > > because the the input must be a vector. Is there anyway to to find all the 
> > > roots of 100 random polynomials without generating each polynomial one by 
> > > one.
> > 
> > Loop over the rows of x and call ROOTS on each row, storing the roots back 
> > into rows or columns of another matrix or into a cell array (depending on 
> > how you need them.)
> > 
> > -- 
> > Steve Lord
> > slord@mathworks.com
> > comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ 
> > 
> How would I wrtie the for loop? Here is what I got so far
> 
> N=100;
> x=zeros(100, 6);    % cretes an empty 100 x 6 matrix
> 
> for k=1:N
>     x(k)=roots(rand([1 6]));
> end
> 
> x
> I know that this won't work so how can I get it to work.
-----------
  You're almost there.  Just add a colon.  And use 100 x 5 size.

N=100;
x=zeros(100, 5);    % creates an empty 100 x 5 matrix
for k=1:N
   x(k,:) = roots(randn([1 6]));
end

Roger Stafford