sustaining_gazes/matlab_version/pdm_generation/nrsfm-em/findG.m

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2016-04-28 21:40:36 +02:00
function G = findG(Rhat)
[F,D] = size(Rhat); F = F/2;
% Build matrix Q such that Q * v = [1,...,1,0,...,0] where v is a six
% element vector containg all six distinct elements of the Matrix C
%clear Q
for f = 1:F,
g = f + F;
h = g + F;
Q(f,:) = zt2(Rhat(f,:), Rhat(f,:));
Q(g,:) = zt2(Rhat(g,:), Rhat(g,:));
Q(h,:) = zt2(Rhat(f,:), Rhat(g,:));
end
% Solve for v
rhs = [ones(2*F,1); zeros(F,1)];
v = Q \ rhs;
% C is a symmetric 3x3 matrix such that C = G * transpose(G)
n = 1;
for x = 1:D,
for y = x:D,
C(x,y) = v(n); C(y,x) = v(n);
n = n+1;
end;
end;
e = eig(C);
%disp(e)
if (any(e<= 0)),
[uu,dd,vv] = svd(C);
G = uu*sqrt(dd);
cc = G*G';
err = sum((cc(:)-C(:)).^2);
%if err>0.03,
if 0 & err>30,
G = [];
dbstack; keyboard
end;
else
G = sqrtm(C);
end
%neg = 0;
%if e(1) <= 0, neg = 1; end
%if e(2) <= 0, neg = 1; end
%if e(3) <= 0, neg = 1; end
%if neg == 1, G = [];
%else G = sqrtm(C);
%end
%-------------------------------------------------
function M = zt2(i,j)
D = length(i);
M = [];
for x = 1:D,
for y = x:D,
if x==y, M = [M, i(x)*j(y)];
else, M = [M, i(x)*j(y)+i(y)*j(x)];
end;
end;
end;