How to show node/element numbers on the boundary ONLY?

I have a function plotting the FE mesh with node numbers and element numbers displayed. An example with (meshx,meshy) = (30,15) shown on the figure below. How do I adpat the code so only node/element numbers on the boundary are displayed?

function plotGrid(meshx, meshy)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Plot FE mesh and diaplay node numbers as well as element numbers
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % Initialization of figure object and variables
    figure('Name', 'Finite Element Mesh', ...
           'Numbertitle','off', ...
           'Position', get(0, 'Screensize'));
    nNodes = (meshx+1)*(meshy+1);
    nElements = (meshx)*(meshy);
    [X_nodes,Y_nodes] = meshgrid(0:meshx, 0:meshy);
    [X_elements,Y_elements] = meshgrid(linspace(0.5, meshx-0.5, meshx), linspace(0.5, meshy-0.5, meshy));
    
    % Plot the grid lines
    plot(X_nodes, Y_nodes, 'k', X_nodes', Y_nodes', 'k');
    title('Finite Element Mesh');
    subtitle({sprintf('(meshx, meshy) = (%i, %i)', meshx, meshy), ''});
    set(gca,'YDir','reverse');
    set(gca,'XTick',[],'YTick',[],'XColor','None','YColor','None');
    
    % Create the lists of node numbers and element numbers
    nodeNumbers = mat2cell(num2str((1:nNodes)'), ones(nNodes,1));
    elementNumbers = mat2cell(num2str((1:nElements)'), ones(nElements,1));
    
    % Insert the labels for node numbers and element numbers
    text(X_nodes(:), Y_nodes(:)+0.1, nodeNumbers, 'FontSize', 8, 'Color', 'k');
    text(X_elements(:)-0.1, Y_elements(:), elementNumbers, 'FontSize', 10, 'FontWeight', 'bold', 'Color', 'r');
end

Answer 1

[Wan Ji]

Hi, friend,

Here are some tips for you.

Firstly, you can find those edges (an edge is generally denoted by two nodes) that are not shared by two elements, so these edges are the boundary edges.

Then collect all the nodes that are attacthed to the boundary edges mentioned above (hint: use unique is very convenient), these nodes are boundary nodes.

Finally, collect all the elements that the boundary nodes belong to, these elements are the boundary elements.

OK, I believe now you understand how to label the boundary nodes and boundary elements.

Do not forget to accept my answer if surely it helps you, thank you.