mat_watan Subroutine

subroutine mat_watan(xr,xi,yr,yi)

! ident_47="@(#)M_LA::mat_watan(3fp): y = atan(x) = (i/2)*log((i+x)/(i-x))"

doubleprecision :: xr
doubleprecision :: xi
doubleprecision :: yr
doubleprecision :: yi
doubleprecision :: tr
doubleprecision :: ti

   if (xi .eq. 0.0d0) then
      yr = datan2(xr,1.0d0)
      yi = 0.0d0
   elseif (xr.ne.0.0d0 .or. dabs(xi).ne.1.0d0) then
      call mat_wdiv(xr,1.0d0+xi,-xr,1.0d0-xi,tr,ti)
      call mat_wlog(tr,ti,tr,ti)
      yr = -(ti/2.0d0)
      yi = tr/2.0d0
   else
      call la_err(32) ! Singularity of LOG or ATAN
   endif

end subroutine mat_watan