assembler.m

function [K, F] = assembler( element_array, t )
%ASSEMBLER Assembles the global stiffness matrix for FEM.
%   Builds cells of the elemental stiffness matrices and elemental force 
%   vectors, then assembles them through the nodal equivalence principle.

%Constructs cells of elemental stiffness matrices and force vectors
N = size(element_array);
K_e = cell(1,N(2));
F_e = cell(1,N(2));
for i = 1:N(2)
    K_e{i} = stiffness_matrix(element_array(i));
    F_e{i} = force_vector(element_array(i));
end

%Assembles stiffness matrix
K = zeros(max(max(t)),max(max(t)));
index = [];
for i = 1:max(max(t))
    for j = 1:max(max(t))
        for e = 1:size(t,1)
            for l = 1:size(t,2)
                if t(e,l) == i
                    index(1) = l;
                end
                if t(e,l) == j
                    index(2) = l;
                end
            end
            if size(index,2) == 2 && index(1) ~= 0
                K(i,j) = K(i,j) + K_e{1,e}(index(1),index(2));
                index = [];
            else
                index = [];
            end
        end
    end
end

%Assembles force vector
F = zeros(max(max(t)),1);
for i = 1:max(max(t))
    for e = 1:size(t,1)
        for l = 1:size(t,2)
            if t(e,l) == i
                F(i,1) = F(i,1) + F_e{1,e}(1,l);
            end
        end
    end
end
end