calculation of kmag

Hi,

I wanted to plot the lightcone by plotting kmag versus k1 and k2 in a
triangular lattice. However, it does not look like a cone(segment).
Plotting it versus sqrt(k1^2+k2^2) works of course. 

Hence, I was looking at the calculation of kmag, but couldn't find it.
E.g. starting from the tri-rods.ctl file, with a small change in the
geometry lattice (reciprocal lattice vectors at 60° from each other)

(set! geometry-lattice (make lattice (size 1 1 sz)
                         (basis1 (/ (sqrt 3) 2) 0.5)
                         (basis2 (/ (sqrt 3) 2) -0.5)))

 one gets that:
k1	k2	k3	kmag/2pi	(comment)
0.3333	0.3333 	0	0.3849		(K-point)
0.5000	0	0	0.5774		(M-point)

However, in this basis, the magnitude of the vector Gamma-K should be
1/sqrt(3), no? Likewise, the M-point is also not giving me the kmag/2pi
value that is shown.

I'm missing something obvious, I'm sure, but I can't find it. Any help?

Thanks!


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