nInterval = INT(xInterval)

          nInterval = 1 + INT( -xInterval/FLOAT(averageCycle(n)) )

          nInterval = nInterval*averageCycle(n) + INT(xInterval) - 1

        nInterval = MOD(nInterval,averageCycle(n))

        IF (dBugFlag.AND.pdiag(n,1,1).NE.nInterval)

     &     ' switch', pdiag(n,1,1),' ->', nInterval, xInterval

        IF ( nInterval.LT.0 .OR. nInterval.GE.averageCycle(n) ) THEN

     &       ' error setting pdiag(n=',n,') to:', nInterval

           pdiag(n,bi,bj) = nInterval

      INTEGER nInterval