Choice of signs/constants in cotmatrix / lscm ? about gptoolbox

[taiya]

Thanks Alec! Now everything is clear, the "-" is because of legacy decisions (in disagreement with how the operator is written on many papers) and the 2_A is to compensate for the fact that your $L=-2_L_{classic}$

Regarding the P for "Flip XY" I see what you mean, I actually did that myself :)
I was just wondering whether it was something I was supposed to do and I was unaware of!

By the way, perhaps you have a better intuition than me.
Any clue on why the following two produce the same result?
(I did this test while I was trying to remove the "Flip XY"):

Q = repdiag(L,2)-2A;
Q = repdiag(L,2)+2A;

[alecjacobson]

I don't think it does, does it? Are you sure you're not also flipping the sign of L, too? Then you'd be comparing Q vs. -Q and my solver (min_quad_with_fixed) will return the same result since it's actually finding a stationary point of the energy (corresponding to the minimum only for positive definite energies Q and maximum for negative definite energies -Q).

[taiya]

Yes, I am sure I am only flipping one (see the zip via email)
I am not using your solver but matlab quadprog.

p.s. do you have anything in matlab to map the outline to a circle?
I wanted to do exercises for both harmonic and LSCM

Thanks!

[alecjacobson]

In your example does it still happen if you have more than two constraints?

On Fri, Nov 4, 2016 at 1:06 PM, Andrea [email protected] wrote:

Yes, I am sure I am only flipping one (see the zip via email)
I am not using your solver but matlab quadprog.

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[taiya]

Very good suggestion for a test :)
Indeed they are different, still puzzling why a result (rather than garbage) is even generated :)
p.s. By the way, did you find a way of showing texture mapped models in matlab?

[alecjacobson]

I never found a satisfying way to show textures on a general triangle mesh using pure matlab.