"be consistent"  
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Re^3: Help with Matrix math!by randyk (Parson) 
on Dec 18, 2007 at 01:41 UTC ( #657583=note: print w/replies, xml )  Need Help?? 
I was thinking of the problem differently 
find the extremal points of
x^{†}Dx, which leads to the eigenvalue
equation Dx = 0. This equation doesn't determine
x^{†}x completely, so one is free to impose, for example, x^{†}x = 1 as a
normalization condition. But you're right that if
x^{†}x = 1 is intended as a true constraint, then a method like Lagrange multipliers should be used.
In Section
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