Boundary conditions of a partial differential equation which are a weighted arithmetic mean of Dirichlet boundary conditions (which specify the value of the function on a surface) and Neumann boundary conditions (which specify the normal derivative of the function on a surface).

Morse, P. M. and Feshbach, H. Methods of Theoretical Physics, Part I. New York: McGraw-Hill, pp. 678-679, 1953.

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Weisstein, Eric W. "Cauchy Boundary Conditions." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/CauchyBoundaryConditions.html