function [K, F] = ApplyRobinBC_mult(model, K, F, alpha, u_out)
mesh = model.Mesh;
nodes = mesh.Nodes;
elements = mesh.Elements;

%Boundary edges
edgesAll = [elements([1 2],:), elements([2 3],:), elements([3 1],:)];
edgesSorted = sort(edgesAll,1);
[edgesUnique,~,ic] = unique(edgesSorted','rows');
counts = accumarray(ic,1);
boundaryEdges = edgesUnique(counts==1,:);   % Nx2 array

for k = 1:size(boundaryEdges,1) %Loop over Robin boundary edges
    i = boundaryEdges(k,1);
    j = boundaryEdges(k,2);

    ri = nodes(1,i);
    rj = nodes(1,j);
    
    %find the edges on the axis -> homogeneous Neumann BC, no Robin contribution
    if ri == 0 && rj == 0
        continue;
    end

    xi = nodes(:,i);
    xj = nodes(:,j);

    L = norm(xi - xj);   % edge length

    % Robin boundary element matrices
    Ke = alpha * L / 6 * [2 1; 1 2];
    Fe = alpha * u_out * L / 2 * [1; 1];

    % Assemble
    K([i j],[i j]) = K([i j],[i j]) + Ke;
    F([i j])       = F([i j]) + Fe;
end
end