sparse matrix assembly without adding duplicate values

A B — Sun, 20 Sep 2009 10:04:02 -0400

Hi

I have three vectors

i_row, j_col, s_val

which I use for assemblying a sparse matrix.
Usually the sparse command adds any elements of s that have duplicate values of i and j together. However I dont want to add up duplicate values. I just want to take the first occurence.

Is there a simple way to way to remove duplicate entries. I tried to come up with something using "unique", but it didnt work. Any other ideas...?

Thanks

Re: sparse matrix assembly without adding duplicate values

John D'Errico — Sun, 20 Sep 2009 11:05:18 -0400

"A B" <gitsnedbutzi@hotmail.com> wrote in message <h94umi$nrk$1@fred.mathworks.com>...
> Hi
>
> I have three vectors
>
> i_row, j_col, s_val
>
> which I use for assemblying a sparse matrix.
> Usually the sparse command adds any elements of s that have duplicate values of i and j together. However I dont want to add up duplicate values. I just want to take the first occurence.
>
> Is there a simple way to way to remove duplicate entries. I tried to come up with something using "unique", but it didnt work. Any other ideas...?
>
> Thanks

That you tried unique and failed does not mean that
unique is not the solution. It simply means that
you used it incorrectly.

This should do the trick, assuming column vectors:

[u_ij,I] = unique([i_row,j_col],'rows','first');
u_s_val = s_val(I);

John

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sparse matrix assembly without adding duplicate values

Re: sparse matrix assembly without adding duplicate values