createBH.m

function [BH, BMother] = createBH(H, HN);
%createBH Creates a boundary topology
%
% USAGE:
%
%       [BH, BMother] = createBH(H, HN);
%
%       [BH, BMother] = createBH(H, createHN(H));
%
%
% DESCRIPTION:
%
%       Given topology H and its neighbourhood HN, will create
%       boundary topology BH.  Can also produce BMother which defines
%       index into H to which boundary element belongs to.
%
%
% INPUT:
%
%       H           - Topology matrix
%       HN          - Neighborhood topology matrix
%
% OUTPUT:
%
%       BH          - Boundary topology matrix
%       BMother     - Vector in which each row defines an index in H to which the
%                     boundary element belongs to
%
% This function is provided with ValoMC

if(size(H,2) > 3)
    if(exist('createBH3') == 0)
        error('Cannot find mex function createBH3. It is located at cpp/3d/createBH3mex.cpp. See installation instructions how to compile it');
    end
    if(nargout > 1)
        error('Cannot create BMother for 3d meshes yet.');
    end
    BH = createBH3(int64(H));

else

    [els, edge] = find(HN == 0);

    BH = zeros(numel(els), 2);
    BMother = zeros(size(BH, 1), 1);

    for(el = 1 : length(BH))
        if(edge(el) == 1)
            BH(el, :) = H( els(el), [1 2]);
            BMother(el) = els(el);
        elseif(edge(el) == 2)
            BH(el, :) = H( els(el), [2 3]);
            BMother(el) = els(el);
        elseif(edge(el) == 3)
            BH(el, :) = H( els(el), [3 1]);
            BMother(el) = els(el);
        end
    end;

%BH=sortBH(BH);

end