
Ublas : 
From: Michael Stevens (mail_at_[hidden])
Date: 20050322 14:43:47
Hi Andreas,
On Tuesday 22 March 2005 14:24, Andreas Klöckner wrote:
>
> A while ago, I tried to change compressed_matrix<> to always have a
> complete index1 array. It occurred to me that this ruins the complexity
> guarantees of the push_back() and pop_back() methods, since then, upon
> each insertion, the filled remainder of the index1 array needs to be
> updated. These methods are important if you're building a
> compressed_matrix from a known and presorted storage pattern, which
> should be lineartime.
OK I understand. I was looking at the insert_element case and not push_back.
One possibility is to work the same way as coordinate_matrix does with its
'sorted_' flag. I suspect a index1_complete function will be the preferred
solution however.
> As a consequence, I'm not so sure any more that enforcing said invariant
> is a good idea.
With a separate function I assume?
> > Do you know if any other compressed matrix libraries yield similarly
> > incomplete index1 array?
>
> I know of none.
That would imply that nothing else has the equivalent of an efficient
push_back. Interesting!
> > I have committed the the operation.hpp patch.
>
> It seems to me you changed the upper loop boundary to "filled1 ()" from
> my patch, which said "filled1 ()  1". I believe your change is
> incorrect: The loop needs to iterate over each row of the matrix.
> index1_data_ has one more entry than the matrix has rows. The leftover
> entry is used to find the end of the last row.
Sorry my sloppyness. The automatic patch application failed. No idea why it
looked like a valid diff. So I applied by hand and missed the change to 1.
Sorry to waste your time on such a stupid mistake.
>
> I've attached a patch to fix this (compressedaxpy20050322.patch).
> The patch also fixes the premultiply (axpy_prod(x, A, ...)) case which I
> had previously forgotten and adds a missing "return v;" that was missing
> from Gunter's recent coordinate_matrix axpy_prod patch.
>
> I've also attached an updated patch against matrix_sparse.hpp
> (completeindex120050322.patch) that adds a fixed, nonconst version
> of complete_index1_array to compressed_matrix. The corresponding
> bindings patch is compressedbindings20050322.patch.
>
> All patches are against CVS as of today.
I'll try and follow this up after Gunters patch!
Michael