FEM 1D General Non Linear Code

FEM 1D General Non Linear Code

I'm trying to build a general 1D FEM solver but i have some problems with the non-linear case. Can anyone help me to fix the code? This is a simple non-optimized code through which I desire to learn the FEM theory. I Used an iterative method (Newton's Method) to solve the nonlinear set of equations. The method starts building the Jacobian matrix.