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Topic: index end-point to matrix
Replies: 6   Last Post: Feb 4, 2013 11:24 AM

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Naresh

Posts: 7
Registered: 12/7/04
Re: index end-point to matrix
Posted: Jan 31, 2013 10:36 AM
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"Jos (10584)" wrote in message <kedggo$ild$1@newscl01ah.mathworks.com>...
> "Naresh Pai" wrote in message <kec3s0$gl9$1@newscl01ah.mathworks.com>...
> > I have a vector with indices, for e.g.
> >
> > b = [1 4 7]
> >
> > Using these indices, I am trying to develop a matrix that looks like this
> > a =[1 0 0;
> > 2 3 4;
> > 5 6 7]
> >
> > In other words, the indices variable (b) indicates end-points of the matrix a for each row. This looks simple but been trying to figure out how to generalize the code when b could be of different sizes. Any hints would be appreciated.
> >
> > Thanks,
> > Naresh

>
> I got confused ... what would A look like if B = [4 1 6 2] for instance?
>
> ~ Jos


Jos, Thanks for your post. B results from a cumsum operation, so it would either ascending (e.g. [1 3 5 9]), or remain constant at some elements ([1 2 2 4]). In the example you provided, the second and fourth element are descending. I have put few other examples to illustrate my requirement. Thanks.

1) b = [2 0 3 4]
a = [1 2;
0 0;
3 0
4 0]

2) b = [ 0 3 7 10]
a = [0 0 0 0;
1 2 3 0;
4 5 6 7;
8 9 10 0]

3) b = [5 0 0]
a = [1 2 3 4 5;
0 0 0 0 0;
0 0 0 0 0]



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