function [Q,c,f,x,info] = quaddecomp(p,z)
%QUADDECOMP Internal function to decompose quadratic expression

[n,m]=size(p);
info = 0;

% Is it a scalar
if (n*m==1)
% Involved in polynomial expression
mt = yalmip('monomtable');
x_lin = getvariables(p);
x_var = find(any(mt(x_lin,:),1));
if nargin==2
x_var = union(x_var,depends(z));
end
x = recover(x_var);
if is(p,'linear')
n = length(x);
Q = spalloc(n,n,0);
fc = getbase(p);
f = fc(1);
if nargin==2
vars = getvariables(p);
c = zeros(length(x),1);
for i = 1:length(vars)
c(find(vars(i)==x_var)) = fc(1+i);
end
else
c = fc(2:end);c=c(:);
end
return
end
degrees = sum(mt(x_lin,:),2);
if all(degrees<=2)
Q = spalloc(length(x),length(x),2*nnz(getbase(p)));
c = zeros(length(x),1);
base = getbase(p);
if nnz(base(1))==0
f = 0;
base = base(2:end);
else
f = base(1);
base = base(2:end);
end

mt = mt(x_lin,x_var);

if 1
[jj,ii,kk] = find(mt');ii = [ii(:) ;0];
top = 1;
for i = 1:length(x_lin)
if ii(top) == ii(top+1)
j = [jj(top) jj(top+1)];
top = top + 2;
else
j = [jj(top)];
top = top + 1;
end
if length(j)==1 % One variable
if kk(top-1)==1
c(j)=base(i);
else
Q(j,j)=Q(j,j) + base(i)/2;
end
else
Q(j(1),j(2))=Q(j(1),j(2)) + base(i)/2;
end
end

else
for i = 1:length(x_lin)
j = find(mt(i,:)); % What variables are used
if length(j)==1 % One variable
if mt(i,j)==1
c(j)=base(i);
else
Q(j,j)=Q(j,j) + base(i)/2;
end
else
Q(j(1),j(2))=Q(j(1),j(2)) + base(i)/2;
end
end
end
Q = Q+Q';
else
if nargout==5
info = 1;
Q = [];
c = [];
f = [];
x = [];
else
error('Function is not quadratic');
end
end

else
if nargout==5
info = 1;
Q = [];
c = [];
f = [];
x = [];
else
error('Function is not scalar');
end
end