Re: Symmetric Matrix Resize

PS = Pete Stieber
PS>> MTL version: mtl-2.1.2-23.tenative
PS>> Compiler: g++ (GCC) 4.1.2 20070925 (Red Hat 4.1.2-27)
PS>> Platform: Fedora 7 x86_64
PS>>
PS>> I'm trying to resize a symmetric matrix using a simple
PS>> test jig called SymmetricPackedResize.cpp ...
PS>>
PS>> #include <mtl/mtl.h>
PS>>
PS>> int main()
PS>> {
PS>>    typedef mtl::matrix<
PS>>      double,
PS>>      mtl::symmetric<mtl::lower>,
PS>>      mtl::packed<> >::type TDSymmetricMatrix;
PS>>
PS>>    TDSymmetricMatrix Symmetric(6, 6);
PS>>
PS>>    Symmetric.resize(16, 16);
PS>>
PS>>    return 0;
PS>> }
PS>>
PS>> I'm compiling with
PS>>
PS>> g++ -IPathToMtlHeaders SymmetricPackedResize.cpp
PS>>
PS>> The first set of errors I receive follow...
Snip
PS>> So the packed_offset class has the dim data member
PS>> declared private.  Looking at the rect_offset class
PS>> for which resize actually works, there is a
PS>> suspicious commenting out for the private: scope
PS>> qualifier ahead of the data members.
PS>>
PS>> I could do the same in packed_offset, but this
PS>> would still leave me with the "packed_offset<...>
PS>> has no member named ld.  It looks like resize
PS>> will only work for rect_offset storage.
PS>>
PS>> Does anyone see a workaround for this?
PS>>
PS>> Peter, does version 4 deal with this?
PS>>
PS>> How do I become an alpha tester of version 4?

PS> Instead of explicitly setting the values of the
PS> offset class in the resize function, I changed
PS> the code to call a new resize member function of
PS> the offset class.  The following code implements
PS> resize for the rect_offset class by performing
PS> the same functionality that was in the dense2D
PS> class resize function.
PS>
PS>  inline void resize(size_type m, size_type n)
PS>  {
PS>    dim = dim_type(m, n);
PS>    ld = n;
PS>  }
PS>
PS> Now I need to add a resize function to the
PS> packed_offset class.  Here's my first cut...
PS>
PS>  inline void resize(size_type m, size_type n)
PS>  {
PS>    dim = dim_type(m, n);
PS>  }
PS>
PS> but the packed_offset class has an addition
PS> data member called bw.  Can anyone explain the
PS> purpose of this data member so I can figure out
PS> if I need to alter it in packed_offset::resize?

OK.  I believe bw stands for band width, as in which bands are required 
with respect to the storage scheme.  My new packed_offset resize now 
looks like the following:

   inline void resize(size_type m, size_type n)
   {
     dim = dim_type(m, n);
     bw = band_type(0, n);
   }

since my symmetric matrix is full.  I also had to modify the storage 
allocation call in dense2d::resize from

     rep_ptr newdata = new reptype(Offset::size(m, n, 0, 0));

to

     rep_ptr newdata = new reptype(Offset::size(m, n, 0, n));

to generate the proper amount of storage for a full symmetric matrix.  A 
general dense matrix using rect_offset doesn't use the last two 
parameters, so it still works.

Unfortunately, I couldn't figure out how to copy the previously existing 
existing matrix elements to the new storage.  The (size_type, size_type) 
operator doesn't work properly at this level of scope.  If anyone can 
help me with that it would be greatly appreciated.

I also noticed that the following code to zero out any extra matrix 
elements if the new matrix is bigger

     for (; i < m; ++i)
       for (; j < n; ++j)
       (*newdata)[i * n + j] = T();

was incorrect and seemed to be unneeded because the allocation code 
seems to zero out the data.

If anyone is interested in a patch to the dense2d.h file that will 
resize both general and symmetric matrices, but will not copy old 
elements, I believe I have one.

If anyone can help me figure out how to copy the old elements, I would 
greatly appreciate it.

Pete

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