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        "description": "Second-order accuracy concerns a symmetric composition of stated evolution operators with sufficient regularity and controlled local/global error. Noncommuting operators need the stated analysis; stiffness, boundaries and nonsmooth solutions can change behavior. It is not a universal stability or convergence guarantee for every split PDE or arbitrary step size.",
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      "statement": "# Strang: split a numerical update without losing second-order accuracy\n\nStrang constructs a half-step/full-step/half-step composition that retains second-order accuracy under the stated smoothness and substep assumptions, with conditional stability and cost comparisons for multidimensional difference schemes.\n\nA complicated simulation can sometimes be divided into simpler updates: move in one direction, then in another. Performing those updates in an arbitrary order introduces an extra error when they do not commute. Strang showed how a symmetric ordering—half of one update, all of the other, then the remaining half—retains second-order accuracy under the paper’s assumptions. The method allows existing one-dimensional difference procedures to become building blocks for multidimensional calculations. The paper treats both a linear wave model and smooth nonlinear systems, and compares accuracy with stability and computational work. A stable component method is still essential; smaller apparent cost does not establish the right physical shock solution. The original explicitly leaves convergence for discontinuous solutions to future progress. This contribution is the ordering and scoped comparison framework, with earlier Lax–Wendroff, Richtmyer and Strang difference methods retained as predecessors.\n\n## Scientific scope\n\nSecond-order accuracy concerns a symmetric composition of stated evolution operators with sufficient regularity and controlled local/global error. Noncommuting operators need the stated analysis; stiffness, boundaries and nonsmooth solutions can change behavior. It is not a universal stability or convergence guarantee for every split PDE or arbitrary step size.\n\n## People and systems\n\nGilbert Strang\n\n\n\n## Original sources\n\n- [Gilbert Strang: On the Construction and Comparison of Difference Schemes,1968original506-517 publictextmirror](https://www.scribd.com/document/230442704/Strang-1968-On-the-Construction-and-Comparison-of-Difference-Schemes)\n- [Gilbert Strang MITbibliography selecteditems11,12,21](https://math.mit.edu/~gs/papers/papers.html)\n",
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