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\end{equation} 
\end{equation} 
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\subsection{Lumping} 
\subsection{Lumping} 
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For \esc, the acceleration solution is prefered as it allows the use of matrix 
For \esc, the acceleration solution is preferred as it allows the use of matrix 
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lumping. Lumping or mass lumping as it is sometimes known, is the process of 
lumping. Lumping or mass lumping as it is sometimes known, is the process of 
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aggressively approximating the density elements of a mass matrix into the main 
aggressively approximating the density elements of a mass matrix into the main 
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diagonal. The use of Lumping is motivaed by the simplicity of diagonal matrix 
diagonal. The use of Lumping is motivated by the simplicity of diagonal matrix 
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inversion. As a result, Lumping can significantly reduce the computational 
inversion. As a result, Lumping can significantly reduce the computational 
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requirements of a problem. Care should be taken however, as this 
requirements of a problem. Care should be taken however, as this 
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function can only be used when the $A$, $B$ and $C$ coefficients of the 
function can only be used when the $A$, $B$ and $C$ coefficients of the 