delzerocolumns.m

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function Xdel = delzerocolumns(X,epsilon,A)
%function Xdel = delzerocolumns(X[,epsilon,A])
% function deleting zero-columns from matrix 'X'.
%
% Detection by `norm^2<\varepsilon`. Optionally, the inner-product-matrix 'A' can be
% additionally passed for correct computation of the inner product.
%
% Parameters:
%  X: matrix whose zero columns shall be eliminated
%  epsilon: tolerance value `\varepsilon`
%  A: optional inner product matrix used for norm computation (Default: `1`)
%
% Return values:
%  Xdel: matrix whose zero columns are deleted

% Bernard Haasdonk 20.7.2006

if nargin<3
  A = 1;
end;

if nargin<2 || isempty(epsilon)
  epsilon=eps;
end;

i = find(sum(X.*(A*X))>epsilon);
if ~isempty(i)
  Xdel = X(:,i);
else
  Xdel=zeros(size(X,1),0);
end;