Figure 5
The matrix is positioned in the center, with each square colored according to its value. The rows and columns of the matrix are arranged in a grid, with the color gradients transitioning from deep purple for lower values to bright yellow for higher values. The row- and column-wise sums are placed on the additional degrees of freedom (adofs), which are positioned at the boundaries of the matrix and are not interpretable as displacements. The bottom and right sides are in deep purple, while the bottom right corner is in yellow. The remaining region is mostly shaded in green and yellow. To the right of the matrix is a color scale that indicates the corresponding values, with the lowest values in deep purple and the highest in yellow. The scale ranges from less than negative 1 times 10 to the 4 power on the bottom to greater than 1 times 10 to the 4 power on the top.Stiffness matrix of a surrogate element with 54 dofs and three additional adofs, NSE = 57. The row- and column-wise sums are placed on the adofs. Hence, they are not interpretable as displacements. Source: Authors’ own work