Re: [Lapackpp-devel] Problem finding Null space using LaSVD_IP()

[Christian S. <sti...@tu...>]

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Good to hear. Feel free to ask more questions if something appears to be
wrong. By the way you should be able to write std::cout<<U_; as well.

Regarding the mailing list address: This is a "mailing list", not a
"forum". You have been sending your emails to the address
"lapackpp-devel-owner (at) lists.sourceforge.net" which is wrong; the
correct email address to send your messages to is
lap...@li... (no -owner)! Thanks.

Christian

Sonia Singhal schrieb:
> hi,
> 
> I think I caught my mistake. I didnt make a copy of the matrix before I
> checked for the homogenous solution. :(
> ~ sonia
> 
> On 12/14/06, *Sonia Singhal * <son...@gm...
> <mailto:son...@gm...>> wrote:
> 
>     Hi,
> 
>     Thanks for the reply.
>     As for posting it on the forum. I had sent the mail to the forum, I
>     have no clue how you have received the mail. I initially emailed it
>     without joining the list and got an error message, maybe thats the
>     reason you got it.
> 
>     As for the problem, even I am not familiar with the algorithms used
>     for svd and am not sure if the null spaces would be the same, but I
>     assumed that since MATLAB also uses LAPACK the answers would be the
>     same.
>     Even if the answers are not the same and I assume that the NULL
>     spaces are returned, then multiplying the original matrix A with a
>     row ( or column ) of VT ( or V ) beyond the rank should be zero. I
>     did this and I got a very high value when I used Norm_Inf(). Whereas
>     in MATLAB I get a very small value ( 10^-14).
> 
>     Also right now I was making small examples ( 3x4, 3x5 ) and what I
>     found was for some examples I am getting right answers and for some
>     they are wrong. By right and wrong I mean comparing both with matlab
>     and checking if A*VT(r,:) is zero.
> 
>     For example :
>     This code / exmaple gives the correct answers
> 
>     //------------------------------------------------------------------------------------------------------
>             // Trying SVD
>             LaGenMatDouble ForSVD(3,5);
>             ForSVD(0,0) = 1;
>             ForSVD(0,1) = 2;
>             ForSVD(0,2) = 3;
>             ForSVD(0,3) = 4;
>             ForSVD(0,4) = 2;
>             ForSVD(1,0) = 2;
>             ForSVD(1,1) = 3;
>             ForSVD(1,2) = 9;
>             ForSVD(1,3) = 2;
>             ForSVD(1,4) = 0;
>             ForSVD(2,0) = 4;
>             ForSVD(2,1) = 5;
>             ForSVD(2,2) = 8;
>             ForSVD(2,3) = 7;
>             ForSVD(2,4) = 4;
>             LaVectorDouble S_(3);
>             LaGenMatDouble U_(3,3), VT_(5,5);
>             LaSVD_IP(ForSVD, S_, U_, VT_);
>             LaVectorDouble x_(5);
>            
>             for(i=0; i<5; ++i){
>                 x_(i) = VT_(4,i);
>             }
>             std::cout << "\tNorm_Inf(A*x)" << Norm_Inf(ForSVD*x_) <<
>     std::endl;
>             std::cout << "U:" << std::endl;
>             for(int i=0; i<3; ++i){
>                 for(int j=0; j<3; ++j){
>                     std::cout << U_(i,j) << " ";
>                 }
>                 std::cout << std::endl;
>             }       
>             std::cout << "V:" << std::endl;
>             for(int i=0; i<5; ++i){
>                 for(int j=0; j<5; ++j){
>                     std::cout << VT_(i,j) << " ";
>                 }
>                 std::cout << std::endl;
>             }
> 
>     //
>     -----------------------------------------------------------------------------------
>     and this doesnt.
>     //
>     -----------------------------------------------------------------------------------
> 
>             // Trying SVD
>             LaGenMatDouble ForSVD(3,5);
>             ForSVD(0,0) = 1;
>             ForSVD(0,1) = 2;
>             ForSVD(0,2) = 3;
>             ForSVD(0,3) = 4;
>             ForSVD(1,0) = 2;
>             ForSVD(1,1) = 3;
>             ForSVD(1,2) = 9;
>             ForSVD(1,3) = 2;
>             ForSVD(2,0) = 4;
>             ForSVD(2,1) = 5;
>             ForSVD(2,2) = 8;
>             ForSVD(2,3) = 7;
>             LaVectorDouble S_(3);
>             LaGenMatDouble U_(3,3), VT_(4,4);
>             LaSVD_IP(ForSVD, S_, U_, VT_);
>             LaVectorDouble x_(5);
>            
>             for(i=0; i<5; ++i){
>                 x_(i) = VT_(4,i);
>             }
>             std::cout << "\tNorm_Inf(A*x)" << Norm_Inf(ForSVD*x_) <<
>     std::endl;
>             std::cout << "U:" << std::endl;
>             for(int i=0; i<3; ++i){
>                 for(int j=0; j<3; ++j){
>                     std::cout << U_(i,j) << " ";
>                 }
>                 std::cout << std::endl;
>             }       
>             std::cout << "V:" << std::endl;
>             for(int i=0; i<4; ++i){
>                 for(int j=0; j<4; ++j){
>                     std::cout << VT_(i,j) << " ";
>                 }
>                 std::cout << std::endl;
>             }
>     //
>     ------------------------------------------------------------------------------------------------
>     Thanks for your time,
>     ~ Sonia

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