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The Skyline solver was initially added for users who build their own copy of FEBio and did not have access to third party linear solvers. It is a sparse direct solver, but not as efficient as Pardiso and not recommended for large problems. When using this solver, it is highly recommended to set the optimize_bw flag in the model file's Control section, which attempts to minimize the matrix bandwidth. It does not require any configuration parameters and only works with symmetric matrices.