## Robertson Condition

For the Helmholtz Differential Equation to be Separable in a coordinate system, the Scale Factors in the Laplacian

 (1)

and the functions and defined by
 (2)

must be of the form of a Stäckel Determinant
 (3)

See also Helmholtz Differential Equation, Laplace's Equation, Separation of Variables, Stäckel Determinant

References

Morse, P. M. and Feshbach, H. Methods of Theoretical Physics, Part 1. New York: McGraw-Hill, p. 510, 1953.