Re: subsums

[Mike Miller]

On Sun, 6 Feb 2005, Dmitri A. Sergatskov wrote:

> Gorazd Brumen wrote:
> > Hi,
> >
> > How do you form a vector of subsums of a certain vector without the for 
> > loop?
> > Example:
> > Let x = [1 2 3 4 5 6 7 8 9 10]
> > I want to get a vector that would have as entries
> > sum([1 2 3 4 5]) and sum ([6 7 8 9 10])?
>
> octave:1> x = [1 2 3 4 5 6 7 8 9 10]
> x =
>
>  1   2   3   4   5   6   7   8   9  10
>
> octave:2> y=reshape(x,5,2)
> y =
>
>  1   6
>  2   7
>  3   8
>  4   9
>  5  10
>
> octave:3> z=sum(y)
> z =
>
> 15  40


Or, in general, for even N:

N=10 (for example)
z=sum(reshape([1:N],N/2,2))
z =

  15  40


Mike



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