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are identical. 
are identical. 
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The displacement solution is depicted in Figure~\ref{FIG LUMPING VALET C}. The 
The displacement solution is depicted in Figure~\ref{FIG LUMPING VALET C}. The 
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domain utilised order $1$ elements (for order $2$ both 
domain utilised order $1$ elements (for order $2$, both 
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lumping methods are unstable). The solutions for the exact and the full mass 
lumping methods are unstable). The solutions for the exact and the full mass 
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matrix approximation are almost identical while the lumping solutions, whilst 
matrix approximation are almost identical while the lumping solutions, whilst 
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identical to each other, exhibit a considerably faster wavefront propagration 
identical to each other, exhibit a considerably faster wavefront propagration 