References

1. T. Abrudan, J. Eriksson, V. Koivunen, ``Conjugate Gradient Algorithm for Optimization Under Unitary Matrix Constraint'', Signal Processing, vol. 89, no. 9, Sep. 2009, pp. 1704-1714.
   available online here
   BibTeX citation here

   
   

2. T. Abrudan, J. Eriksson, V. Koivunen; ``Steepest Descent Algorithm for Optimization under Unitary Matrix Constraint'', IEEE Transactions on Signal Processing, vol. 56, no. 3, Mar. 2008, pp. 1134-1147.
   available online here
   BibTeX citation here