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[Lapack] QR in Lapack


I am trying to use DGEQR2 to calculate QR factorization of a rectangular 
matrix.  I was able to compile the library and run it with a simple 4x3 case. I 
also could see R (which is the upper triangular portion of A on exit).  
However, I am having some issue on extracting Q from the matrix.

In the documentation it is written that Q is the product of elementary 
reflectors (H(1)H(2)...H(k)), where H(i) = I - tau*v*v_transpose and v is 
stored in the lower triangular portion of A on exit. This involves a lot of 
calculations outside the library.  Is there any easier way to calculate Q? I am 
not sure about what are the properties of elementary reflectors and properties 
of v, we can use to simplify the calculations.

Any help in this matter will be greatly appreciated.


Associate Professor                                                             
Mailing Address:
Mechanical Engineering/UAB                                                     
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