Truss 3D (Tetrahedral) using FEM (direct stiffness)

Deformation of a tetrahedral truss (4 nodes and 6 elements) with 3 pinned bottom nodes and downward force applied to the top node

%% System of Connected 6 Bar Elements / Truss (Tetrahedron) in 3D
% Units: force = N; displacement = m; stiffness = N/m; modulus = Pa
% by Prof. Roche C. de Guzman
clear; clc; close('all');
%% Given
% Degrees of Freedom (DOF), Side length, Node Coordinates, and Order
dim = 3; DOF = dim; ang = pi/6; s = 2;
n1 = [0 0 0]; n2 = [0 s 0]; n3 = [s*cos(ang) s*sin(ang) 0]; n4 = [(s*(3^0.5)/6) (s/2) s*sin(acos((3^0.5)/3))];
n = {n1 n2 n3 n4}; nodes = [1 3; 3 2; 2 1; 1 4; 4 3; 4 2]; % pair of nodes per element