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Fernando Casas studied operator splitting with Sergio Blanes and Ander Murua. Their work constructs higher-order compositions using complex coefficients with positive real parts. The approach addresses the negative-step obstruction of real-coefficient splittings, making high-order integration possible in settings where backward evolution, such as backward diffusion, is problematic.^[ref]

Sergio Blanes coauthored methods for splitting differential-equation evolution with Fernando Casas and Ander Murua. They studied complex composition coefficients with positive real parts, avoiding the backward real-time steps required by higher-order real splittings. This matters for parabolic partial differential equations, where a backward diffusion substep can be ill posed.^[ref]