Assembling local stiffness matrices to global matrice.

Hello, I have a truss system consisting of 10 elements. I need to find the optimum solution for the section areas which results a specific maximum displacement by F. Here is my question:

The elements are in 2 degrees of freedom system.I wrote the local stiffness matrices (4x4) of each element, but I don't know how to assemble them into (12x12) global stiffness matrix.

[Jan]

Is this a Matlab question or does it concern the scientific part of mechanics?

[yasin bestas]

It concern the mechanics. I wrote stiffness matrix for each element and need to assemble them. Some nodes are common, e.g, node 2 is common for 1st, 2nd, 6th, 8th and 10th. elements for below image. Should I sum the terms in matrices that represents in identic nodes? Or is there a different method?