International Journal of Computer Mathematics
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We derive the explicit expressions of the normwise structured backward errors of saddle point systems; we extend the previous results of Sun [Linear Algebra Appl., 288 (1999), pp. 75-88] to a general $2 \times 2$ block linear system, where the (1,1) block is general and not symmetric. We also compare the structured backward error with the unstructured one and find that the difference can be arbitrarily large.