Title of program: HYDELP Nature of physical problem In geophysics the first order ellipticity of a planet is often Catalogue number: ACZT required for a given model. In this new method the hydrostatic ellipticity of a planet can be calculated as a function Program obtainable from: CPC Program Library, Queen's of the mean radius. The input data needed are a set of values University of Belfast, N. Ireland (see application form in this of the density of the planet as a function of the mean radius. issue) The density model may have several jump discontinuities. Computer: IBM 3033 Method of solution The density model (with or without jump discontinuities) is Installation: University of Toronto Computing Center interpolated by cubic [-lermite basis functions and the Darwin-dc Sitter-Radau transformed first order ellipticity Operating system: Os equation is integrated exactly to obtain the solution [1,2]. The numerical error is limited to that of the interpolation of Program language used: FORTRAN IV the density model which is very small [3]. High speed storage required: 51 Kbytes Restrictions on the complexity of the problem As far as the theory is valid there are no known restrictions. No. of bits in a byte: 8 The number of model points and the jump discontinuities may be set by users. Overlay structure: none Typical running time No. of tapes required: none 0.28 s for test run.