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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+# AMED4 -- Median of four vectors.  Each output point M[i] is the median of the
+# four input points A[i],B[i],C[i],D[i].  The vector min and max are also
+# computed and returned in the A and D vectors.  The input vectors are modifed
+# in place.
+
+procedure amed4s (a, b, c, d, m, npix)
+
+short	a[ARB], b[ARB]		# input vectors
+short	c[ARB], d[ARB]		# input vectors
+short	m[ARB]				# output vector (median)
+int	npix
+
+int	i
+short	temp
+define	swap {temp=$1;$1=$2;$2=temp}
+
+begin
+	do i = 1, npix {
+	    # Move the minimum value to A[i].
+	    if (b[i] < a[i])
+		swap (b[i], a[i])
+	    if (c[i] < a[i])
+		swap (c[i], a[i])
+	    if (d[i] < a[i])
+		swap (d[i], a[i])
+
+	    # Move the maximum value to D[i].
+	    if (b[i] > d[i])
+		swap (b[i], d[i])
+	    if (c[i] > d[i])
+		swap (c[i], d[i])
+
+	    # Return the median value.
+	    if (b[i] < c[i])
+		m[i] = b[i]
+	    else
+		m[i] = c[i]
+	}
+end