SUBROUTINE XSPMU(NU1,NU2,MU1,MU2,THETA,X,SX,ID,PQA,IPQA)
C***BEGIN PROLOGUE  XSPMU
C***REFER TO  XSLEGF
C***ROUTINES CALLED  XSADD, XSADJ, XSPQNU
C***DATE WRITTEN   820728   (YYMMDD)
C***REVISION DATE  871119   (YYMMDD)
C***CATEGORY NO.  C3a2,C9
C***KEYWORDS  LEGENDRE FUNCTIONS
C***AUTHOR  SMITH, JOHN M. (NBS AND GEORGE MASON UNIVERSITY)
C***PURPOSE  TO COMPUTE THE VALUES OF LEGENDRE FUNCTIONS FOR XSLEGF.
C METHOD: BACKWARD MU-WISE RECURRENCE FOR P(-MU,NU,X) FOR FIXED NU TO
C         OBTAIN P(-MU2,NU1,X),P(-(MU2-1),NU1,X),....,P(-MU1,NU1,X)
C         AND STORE IN ASCENDING MU ORDER.
C***REFERENCES  OLVER AND SMITH,J.COMPUT.PHYSICS,51(1983),N0.3,502-518.
C***END PROLOGUE  XSPMU