Documentation of the Physical space Statistical Analysis System PSAS Part I The Conjugate Gradient Solver Version PSAS

This document describes Version of the conjugate gradient solver component of DAO s Physical space Statistical Analysis System PSAS An overview of the general PSAS algorithm is presented followed by an outline of the pre conditioned conjugate gradient algorithm and its implementation in PSAS A description of the main For tran subroutines related to the conjugate gradient solver is given with the source code listed in the Appendix This O ce Note focuses on a particular aspect of the PSAS algorithm namely the conjugate gradient solver The details of the observation and forecast error covariance modeling the strategies for parallelization and domain decomposition data ow and user inetrface will be described in subsequent DAO O ce Notes The emphasis of this document is on software design and implementation and not on the scienti c aspects of PSAS which will be documented elsewhere An on line version of this document can be obtained from ftp dao gsfc nasa gov pub office notes on ps Z postscript ftp niteroi gsfc nasa gov www on on html HTML Visit also the data Assimilation O ce s Home Page at http dao gsfc nasa gov