DOUBLE PRECISION FUNCTION iau_EORS ( RNPB, S ) *+ * - - - - - - - - - * i a u _ E O R S * - - - - - - - - - * * Equation of the origins, given the classical NPB matrix and the * quantity s. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: support routine. * * Given: * RNPB d(3,3) classical nutation x precession x bias matrix * S d the quantity s (the CIO locator) * * Returned: * iau_EORS d the equation of the origins in radians. * * Notes: * * 1) The equation of the origins is the distance between the true * equinox and the celestial intermediate origin and, equivalently, * the difference between Earth rotation angle and Greenwich * apparent sidereal time (ERA-GST). It comprises the precession * (since J2000.0) in right ascension plus the equation of the * equinoxes (including the small correction terms). * * 2) The algorithm is from Wallace & Capitaine (2006). * * References: * * Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855 * * Wallace, P. & Capitaine, N., 2006, A&A (submitted) * * This revision: 2006 November 2 * * Copyright (C) 2007 IAU SOFA Review Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION RNPB(3,3), S DOUBLE PRECISION X, AX, XS, YS, ZS, P, Q * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Evaluate Wallace & Capitaine (2006) expression (16). X = RNPB(3,1) AX = X / ( 1D0 + RNPB(3,3) ) XS = 1D0 - AX*X YS = -AX*RNPB(3,2) ZS = -X P = RNPB(1,1)*XS + RNPB(1,2)*YS + RNPB(1,3)*ZS Q = RNPB(2,1)*XS + RNPB(2,2)*YS + RNPB(2,3)*ZS IF ( P.NE.0D0 .OR. Q.NE.0D0 ) THEN iau_EORS = S - ATAN2 ( Q, P ) ELSE iau_EORS = S END IF * Finished. *+---------------------------------------------------------------------- * * Copyright (C) 2007 * Standards Of Fundamental Astronomy Review Board * of the International Astronomical Union. * * ===================== * SOFA Software License * ===================== * * NOTICE TO USER: * * BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING TERMS AND CONDITIONS * WHICH APPLY TO ITS USE. * * 1. The Software is owned by the IAU SOFA Review Board ("the Board"). * * 2. The Software is made available free of charge for use by: * * a) private individuals for non-profit research; and * * b) non-profit educational, academic and research institutions. * * 3. Commercial use of the Software is specifically excluded from the * terms and conditions of this license. Commercial use of the * Software is subject to the prior written agreement of the Board on * terms to be agreed. * * 4. The provision of any version of the Software under the terms and * conditions specified herein does not imply that future versions * will also be made available under the same terms and conditions. * * 5. The user may modify the Software for his/her own purposes. The * user may distribute the modified software provided that the Board * is informed and that a copy of the modified software is made * available to the Board on request. All modifications made by the * user shall be clearly identified to show how the modified software * differs from the original Software, and the name(s) of the * affected routine(s) shall be changed. The original SOFA Software * License text must be present. * * 6. In any published work produced by the user and which includes * results achieved by using the Software, the user shall acknowledge * that the Software was used in producing the information contained * in such publication. * * 7. The user may incorporate or embed the Software into other software * products which he/she may then give away free of charge but not * sell provided the user makes due acknowledgement of the use which * he/she has made of the Software in creating such software * products. Any redistribution of the Software in this way shall be * made under the same terms and conditions under which the user * received it from the SOFA Center. * * 8. The user shall not cause the Software to be brought into * disrepute, either by misuse, or use for inappropriate tasks, or by * inappropriate modification. * * 9. The Software is provided to the user "as is" and the Board makes * no warranty as to its use or performance. The Board does not and * cannot warrant the performance or results which the user may * obtain by using the Software. The Board makes no warranties, * express or implied, as to non-infringement of third party rights, * merchantability, or fitness for any particular purpose. In no * event will the Board be liable to the user for any consequential, * incidental, or special damages, including any lost profits or lost * savings, even if a Board representative has been advised of such * damages, or for any claim by any third party. * * Correspondence concerning SOFA software should be addressed as * follows: * * Internet email: sofa@rl.ac.uk * Postal address: IAU SOFA Center * Rutherford Appleton Laboratory * Chilton, Didcot, Oxon OX11 0QX * United Kingdom * * *----------------------------------------------------------------------- END