function save_mesh2_mini( xc, ia, e, basename)
% Save the 3D triangular mesh in the minimal way (only coordinates and vertex connectivity)
% in binary file.
% The indexing in the connectivity is changed to C-style (starts with 0)
%
% coordinates  xc: [2][nnode]
% connectivity ia: [4][nelem]   with  t(4,:) are the subdomain numbers
% edges         e: [7][nedges]  boundary edges
%                              e([1,2],:) - start/end vertex of edge
%                              e([3,4],:) - start/end values
%                              e(5,:)     - segment number
%                              e([6,7],:) - left/right subdomain
%        basename: file name without extension
% data from
% output from <https://de.mathworks.com/help/pde/ug/initmesh.html initmesh>
%
fname = [basename, '.bin'];
offset = 1;         % index difference from C to Matlab

nnode = size(xc,2);
ndim  = size(xc,1);
nelem = size(ia,2);
nvert_e = 3;

fileID = fopen(fname,'w');
fwrite(fileID, nnode, 'int');          % number of nodes
fwrite(fileID, ndim,  'int');          % space dimension
fwrite(fileID, nelem, 'int');          % number of elements
fwrite(fileID, nvert_e, 'int');        % number of vertices per element

fwrite(fileID, xc(:), 'double');       % coordinates
tmp=ia(1:3,:)-offset;
fwrite(fileID, tmp(:), 'double');      % connectivity

end