function Q = diagadd(Q,v)

% DIAGADD   Computes the sum of a matrix and a diagonal scalar entry.
%
% [Q] = DIAGADD(X,v)
%
% This function adds scalar quantities diagonally to a square matrix. It is
% also equivalent to Q = X + v*eye(length(X)), where v is the scalar to be
% added onto the diagonal matrix X, but in a much more efficient manner.
% 
% Inputs:
%       X   = Any square matrix
%       v   = Scalar variable
%
% Output:
%       Q   = Result of summation
%
%
% (C) Gaussian Process Toolbox 1.0
% (C) Copyright 2005-2007, Keith Neo <keith.neo@nuim.ie>
%                          http://www.hamilton.ie

[N1,N2]=size(Q);
if N1==N2
    for i=1:N1
        Q(i,i)=Q(i,i)+v;
    end
else
    disp('Matrix is not a square matrix');
    clear Q;
end