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+#include "erfa.h"
+
+void eraBp00(double date1, double date2,
+ double rb[3][3], double rp[3][3], double rbp[3][3])
+/*
+** - - - - - - - -
+** e r a B p 0 0
+** - - - - - - - -
+**
+** Frame bias and precession, IAU 2000.
+**
+** Given:
+** date1,date2 double TT as a 2-part Julian Date (Note 1)
+**
+** Returned:
+** rb double[3][3] frame bias matrix (Note 2)
+** rp double[3][3] precession matrix (Note 3)
+** rbp double[3][3] bias-precession matrix (Note 4)
+**
+** Notes:
+**
+** 1) The TT date date1+date2 is a Julian Date, apportioned in any
+** convenient way between the two arguments. For example,
+** JD(TT)=2450123.7 could be expressed in any of these ways,
+** among others:
+**
+** date1 date2
+**
+** 2450123.7 0.0 (JD method)
+** 2451545.0 -1421.3 (J2000 method)
+** 2400000.5 50123.2 (MJD method)
+** 2450123.5 0.2 (date & time method)
+**
+** The JD method is the most natural and convenient to use in
+** cases where the loss of several decimal digits of resolution
+** is acceptable. The J2000 method is best matched to the way
+** the argument is handled internally and will deliver the
+** optimum resolution. The MJD method and the date & time methods
+** are both good compromises between resolution and convenience.
+**
+** 2) The matrix rb transforms vectors from GCRS to mean J2000.0 by
+** applying frame bias.
+**
+** 3) The matrix rp transforms vectors from J2000.0 mean equator and
+** equinox to mean equator and equinox of date by applying
+** precession.
+**
+** 4) The matrix rbp transforms vectors from GCRS to mean equator and
+** equinox of date by applying frame bias then precession. It is
+** the product rp x rb.
+**
+** 5) It is permissible to re-use the same array in the returned
+** arguments. The arrays are filled in the order given.
+**
+** Called:
+** eraBi00 frame bias components, IAU 2000
+** eraPr00 IAU 2000 precession adjustments
+** eraIr initialize r-matrix to identity
+** eraRx rotate around X-axis
+** eraRy rotate around Y-axis
+** eraRz rotate around Z-axis
+** eraCr copy r-matrix
+** eraRxr product of two r-matrices
+**
+** Reference:
+** "Expressions for the Celestial Intermediate Pole and Celestial
+** Ephemeris Origin consistent with the IAU 2000A precession-
+** nutation model", Astron.Astrophys. 400, 1145-1154 (2003)
+**
+** n.b. The celestial ephemeris origin (CEO) was renamed "celestial
+** intermediate origin" (CIO) by IAU 2006 Resolution 2.
+**
+** Copyright (C) 2013-2014, NumFOCUS Foundation.
+** Derived, with permission, from the SOFA library. See notes at end of file.
+*/
+{
+/* J2000.0 obliquity (Lieske et al. 1977) */
+ const double EPS0 = 84381.448 * ERFA_DAS2R;
+
+ double t, dpsibi, depsbi, dra0, psia77, oma77, chia,
+ dpsipr, depspr, psia, oma, rbw[3][3];
+
+
+/* Interval between fundamental epoch J2000.0 and current date (JC). */
+ t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC;
+
+/* Frame bias. */
+ eraBi00(&dpsibi, &depsbi, &dra0);
+
+/* Precession angles (Lieske et al. 1977) */
+ psia77 = (5038.7784 + (-1.07259 + (-0.001147) * t) * t) * t * ERFA_DAS2R;
+ oma77 = EPS0 + ((0.05127 + (-0.007726) * t) * t) * t * ERFA_DAS2R;
+ chia = ( 10.5526 + (-2.38064 + (-0.001125) * t) * t) * t * ERFA_DAS2R;
+
+/* Apply IAU 2000 precession corrections. */
+ eraPr00(date1, date2, &dpsipr, &depspr);
+ psia = psia77 + dpsipr;
+ oma = oma77 + depspr;
+
+/* Frame bias matrix: GCRS to J2000.0. */
+ eraIr(rbw);
+ eraRz(dra0, rbw);
+ eraRy(dpsibi*sin(EPS0), rbw);
+ eraRx(-depsbi, rbw);
+ eraCr(rbw, rb);
+
+/* Precession matrix: J2000.0 to mean of date. */
+ eraIr(rp);
+ eraRx(EPS0, rp);
+ eraRz(-psia, rp);
+ eraRx(-oma, rp);
+ eraRz(chia, rp);
+
+/* Bias-precession matrix: GCRS to mean of date. */
+ eraRxr(rp, rbw, rbp);
+
+ return;
+
+}
+/*----------------------------------------------------------------------
+**
+**
+** Copyright (C) 2013-2014, NumFOCUS Foundation.
+** All rights reserved.
+**
+** This library is derived, with permission, from the International
+** Astronomical Union's "Standards of Fundamental Astronomy" library,
+** available from http://www.iausofa.org.
+**
+** The ERFA version is intended to retain identical functionality to
+** the SOFA library, but made distinct through different function and
+** file names, as set out in the SOFA license conditions. The SOFA
+** original has a role as a reference standard for the IAU and IERS,
+** and consequently redistribution is permitted only in its unaltered
+** state. The ERFA version is not subject to this restriction and
+** therefore can be included in distributions which do not support the
+** concept of "read only" software.
+**
+** Although the intent is to replicate the SOFA API (other than
+** replacement of prefix names) and results (with the exception of
+** bugs; any that are discovered will be fixed), SOFA is not
+** responsible for any errors found in this version of the library.
+**
+** If you wish to acknowledge the SOFA heritage, please acknowledge
+** that you are using a library derived from SOFA, rather than SOFA
+** itself.
+**
+**
+** TERMS AND CONDITIONS
+**
+** Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions
+** are met:
+**
+** 1 Redistributions of source code must retain the above copyright
+** notice, this list of conditions and the following disclaimer.
+**
+** 2 Redistributions in binary form must reproduce the above copyright
+** notice, this list of conditions and the following disclaimer in
+** the documentation and/or other materials provided with the
+** distribution.
+**
+** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
+** the International Astronomical Union nor the names of its
+** contributors may be used to endorse or promote products derived
+** from this software without specific prior written permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+** POSSIBILITY OF SUCH DAMAGE.
+**
+*/