\begin{itemize}
\item \textbf{Equilibrium Condition} It represents the internal forces on the interface of component $A$ are equal but opposite to the forces on the interface of component $B$. As shown in Figure ???? and equation (?????)
\end{itemize}
\begin{equation}
g^{A}_{b}=-g^{B}_{b}
\end{equation}
The LM-FBS method extends Equation () by stating that the interface internal forces are denoted by some Lagrange multipliers shown in Figure (). Equation () shows the relation between the internal forces $g$ and the Lagrange multipliers.
\begin{equation}
g=B^{T}\lambda
\end{equation}
The matrix notation will form by substituting of equation () in () and by adding the compatibility condition of equation () as bellow:
\\***equation**\\
The presented system of equations is solved for the coupled displacements $u$. The derivation is below:
\\***eq*****\\
