Re: another quick question

Opps,
Nevermind - simply using  Matrix::OneDRef's in your swap_row function 
*does* work, I just forgot to undo the changes I had made to my copy of 
mtl::swap.

-Sven

At 09:06 AM 12/3/2003 -0500, you wrote:
>Thanks Rich,
>
>Your code was very helpful, though MSVC6 has some issues with it.
>
>More exactly, it considers
>Matrix::OneD A0 = A[i];
>To be an assignment between incompatible types.
>
>Using Matrix::OneDRef instead of Matrix::OneD gets rid of the compiler 
>error, but simply substituting OneDRef's into your code leads to the same 
>old crash.
>
>I've failed to find a simple modification of your swap_row function which 
>will work under MSVC6, but I have figured out how to do the swap "by 
>hand"; which ought to be good enough given my limited purposes.
>
>-Sven
>
>struct dn {
>         double d;
>         int n;
>         dn(double d, int n) : d(d), n(n) {}
>};
>
>//much slower than it needs to be, but still potentially faster than using 
>dense matrices...
>void swap_row(Matrix& A, int i, int j) {
>
>         std::vector<dn> A0;
>         std::vector<dn> A1;
>
>         Matrix::OneDRef::iterator r;
>         for(r=A[i].begin();r!=A[i].end();r++)
>                 A0.push_back(dn(*r,r.index()));
>         for(r=A[j].begin();r!=A[j].end();r++)
>                 A1.push_back(dn(*r,r.index()));
>
>         A[i].clear();
>         A[j].clear();
>
>         std::vector<dn>::iterator s;
>         for(s=A0.begin();s!=A0.end();s++)
>                 A[j].push_back(s->n,s->d);
>         for(s=A1.begin();s!=A1.end();s++)
>                 A[i].push_back(s->n,s->d);
>}
>
>At 10:27 PM 12/2/2003 -0800, liequan wrote:
>>Hi Sven,
>>
>>The following code compiles and runs correctly wiht gcc 3.3 for swapping
>>two rows in array compressed1D matrix. It is not constant time though.
>>
>>#include "mtl/matrix.h"
>>#include "mtl/mtl.h"
>>#include "mtl/utils.h"
>>#include <algorithm>
>>
>>using namespace mtl;
>>
>>typedef matrix< double, rectangle<>, array< compressed<> >,
>>row_major >::type Matrix;
>>
>>void
>>swap_row(Matrix& A, int i, int j)
>>{
>>   Matrix::OneD A0 = A[i];
>>   Matrix::OneD A1 = A[j];
>>   mtl::swap(A0, A1);
>>   typedef Matrix::OneD::size_type I;
>>   std::vector<I>& A0n = const_cast<std::vector<I>&>(A0.nz_struct());
>>   std::vector<I>& A1n = const_cast<std::vector<I>&>(A1.nz_struct());
>>   std::swap(A0n, A1n);
>>}
>>
>>int main ()
>>{
>>    //initialize the matrix
>>    const int size=4;
>>    Matrix A(size,size);
>>    A(0,0)=1;
>>    A(1,2)=2;
>>    A(3,1)=5;
>>    A(0,3)=3;
>>
>>    swap_row(A, 0, 1);
>>
>>    print_all_matrix(A);
>>    return 0;
>>}
>>
>>Andy, I am sorry for misleading information -- I was wrong about
>>swapping. In fact, only dense matrices/dense vectors are taken care by
>>mtl::swap in mtl2.
>>
>>--Rich Lee
>>
>>
>>On Tue, 2003-12-02 at 20:38, Sven Olsen wrote:
>> > At 07:49 PM 12/2/2003 -0500, you wrote:
>> > >I think this example code should swap the two rows in constant time.
>> >
>> > Hmm.  Well, the example code I gave crashes in terrible ways...  I assumed
>> > it was breaking because I wasn't using the library properly, but if you
>> > think it should work, then something is going wrong...
>> >
>> > I've done a little investigation, and it looks like the problems that I've
>> > been running into with row swapping are most likely due to the fact that
>> > the mtl::swap functions will swap the value vectors of two compressed
>> > arrays, but not the index vectors (which leads to all sorts of interesting
>> > problems).
>> > I have started hacking around with a solution to use in my own code, but I
>> > don't know my way around the MTL source, so even if I get something
>> > working, it's probably not going to be pretty.
>> >
>> >  From what I've seen, this is something that anyone who knew the MTL 
>> source
>> > fairly well would have little trouble fixing.
>> >
>> > Here's the code that crashes in terrible ways:
>> >
>> > #include "mtl/matrix.h"
>> > #include "mtl/mtl.h"
>> > #include "mtl/utils.h"
>> >
>> > using namespace mtl;
>> >
>> > typedef matrix< double, rectangle<>, array< compressed<> >,
>> > row_major >::type Matrix;
>> >
>> > int main ()
>> > {
>> >    using std::cout;
>> >    using std::endl;
>> >
>> >    //initialize the matrix
>> >    const int size=4;
>> >    Matrix A(size,size);
>> >    A(0,0)=1;
>> >    A(1,2)=2;
>> >    A(3,1)=5;
>> >    A(0,3)=3;
>> >
>> >    //swap the first two rows
>> >    mtl::swap(A[0],A[1]);
>> >
>> >    //output the results
>> >    for (int ii=0; ii<A.nrows(); ii++) {
>> >      for (int j=0; j<A.ncols(); j++) {
>> >        cout.width(6);
>> >        cout << A(ii, j) << " ";
>> >      }
>> >          cout << endl;
>> >    }
>> >
>> >    return 0;
>> > }
>> >
>> > The output that I get is:
>> >
>> > 2       0       0       2.10535e-314
>> > 0       0       1       0
>> > 0       0       0       0
>> > 0       5       0       0
>> >
>> > I then crash while trying to execute the cleanup function "_free_dbg".
>> >
>> > A little more experimenting indicates that while I am swapping the value
>> > vectors, I'm not swapping the index vectors-
>> > So the matrix defined by
>> >    Matrix A(2,2);
>> >    A(0,0)=1;
>> >    A(1,2)=2;
>> > Swaps rows without trouble (which makes sense because the index 
>> vectors are
>> > the same for each row)
>> >
>> > While swapping the rows in
>> >    Matrix A(2,4);
>> >    A(0,0)=1;
>> >    A(1,2)=2;
>> >    A(1,1)=6;
>> >    A(0,3)=3;
>> >
>> > Yeilds
>> > 6       0       0       2
>> > 0       1       3       0
>> >
>> > when it clearly should give
>> > 0       6       2       0
>> > 1       0       0       3
>> >
>> > Thanks for your help,
>> >          Sven
>> >
>> >
>> > >On Dec 2, 2003, at 5:31 PM, Sven Olsen wrote:
>> > >
>> > >>If I am working with a matrix of type:
>> > >>
>> > >>typedef matrix< double, rectangle<>, array< compressed<> >,
>> > >>row_major >::type Matrix;
>> > >>
>> > >>what is the easiest way to swap two of the rows?
>> > >>
>> > >>I.E., I want to do something like
>> > >>Matrix A(4,4);
>> > >>/*initialize A*/
>> > >>swap(A[0],A[1]);
>> > >>
>> > >>Thanks,
>> > >>         Sven
>> > >>
>> > >>_______________________________________________
>> > >>This list is archived at http://www.osl.iu.edu/MailArchives/mtl-devel/
>> > >
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>> >
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>
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