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+.help xy2xy Jun99 "Slalib Package"
+.nf
+
+      SUBROUTINE slXYXY (X1,Y1,COEFFS,X2,Y2)
+
+     - - - - - -
+      X Y X Y
+     - - - - - -
+
+  Transform one [X,Y] into another using a linear model of the type
+  produced by the slFTXY routine.
+
+  Given:
+     X1       d        x-coordinate
+     Y1       d        y-coordinate
+     COEFFS  d(6)      transformation coefficients (see note)
+
+  Returned:
+     X2       d        x-coordinate
+     Y2       d        y-coordinate
+
+  The model relates two sets of [X,Y] coordinates as follows.
+  Naming the elements of COEFFS:
+
+     COEFFS(1) = A
+     COEFFS(2) = B
+     COEFFS(3) = C
+     COEFFS(4) = D
+     COEFFS(5) = E
+     COEFFS(6) = F
+
+  the present routine performs the transformation:
+
+     X2 = A + B*X1 + C*Y1
+     Y2 = D + E*X1 + F*Y1
+
+  See also slFTXY, slPXY, slINVF, slDCMF
+
+  P.T.Wallace   Starlink   5 December 1994
+
+  Copyright (C) 1995 Rutherford Appleton Laboratory
+  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+
+.fi
+.endhelp