regular_submatrix_indices.m

function indices = regular_submatrix_indices(M,epsilon)
%function indices = regular_submatrix:indices(M,epsilon)
%
% function determining the indices of a submatrix of the square
% matrix M, such that M(indices,indices) is a regular matrix with 
% determinant larger
% than epsilon. For this, simple matrix-growing is performed
% starting with the left upper element. If 
% addition of a row/column leads to too-small determinant, this is skipped.
%
% this routine can be applied on gram-matrices to detect linear
% independent vectors.

% Bernard Haasdonk 14.11.2007

indices = 1;

for j = 2:size(M,1);
  ind_new = [indices, j];
  B = M(ind_new,ind_new);
  if abs(det(B))>=epsilon
    % add j row/column
    indices = ind_new;
  end
end

% TO BE ADJUSTED TO NEW SYNTAX
%| \docupdate