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diff --git a/sys/mwcs/mwopen.x b/sys/mwcs/mwopen.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<syserr.h>
+include	<error.h>
+include	"mwcs.h"
+
+# MW_OPEN -- Create a new MWCS descriptor.  If the non-NULL address of a
+# buffer containing a saved MWCS is given, the saved MWCS will be loaded,
+# otherwise a unitary MWCS of the indicated dimension is created.
+
+pointer procedure mw_open (bufptr, ndim)
+
+pointer	bufptr		#I pointer to encoded MWCS, or NULL
+int	ndim		#I dimension of system to be created
+
+int	i
+pointer	mw, wp
+int	mw_allocd()
+errchk	calloc, mw_load, syserrs, mw_allocd
+string	s_physical "physical"
+
+begin
+	# Initialize the function drivers.
+	call wf_init()
+
+	# Allocate the base descriptor.
+	call calloc (mw, LEN_MWCS, TY_STRUCT)
+
+	# Load saved MWCS, if one was given.
+	if (bufptr != NULL) {
+	    call mw_load (mw, bufptr)
+	    return (mw)
+	}
+
+	# Initialize the new descriptor to a unitary transform of dimension
+	# NDIM.  Most of this is accomplished by merely creating a zeroed
+	# descriptor.
+
+	if (ndim < 1 || ndim > MAX_DIM) {
+	    call mfree (mw, TY_STRUCT)
+	    call syserrs (SYS_MWNDIM, "mw_open")
+	}
+
+	MI_MAGIC(mw) = MWCS_MAGIC
+	MI_NDIM(mw) = ndim
+	MI_NLOGDIM(mw) = ndim
+	MI_LTV(mw) = mw_allocd (mw, ndim)
+	MI_LTM(mw) = mw_allocd (mw, ndim * ndim)
+	call mw_mkidmd (D(mw,MI_LTM(mw)), ndim)
+	do i = 1, ndim {
+	    MI_AXNO(mw,i) = i
+	    MI_PHYSAX(mw,i) = i
+	}
+
+	# Set up the builtin world systems "physical" and "logical".
+	# Both are linear systems.  The physical system is a unitary
+	# transformation (since world systems are defined relative to
+	# the physical system), and the logical system has the Lterm
+	# for its linear term.  No wcs attributes other than wtype are
+	# defined.
+
+	# Create the physical system.
+	call mw_newsystem (mw, s_physical, ndim)
+	do i = 1, ndim
+	    call mw_swtype (mw, i, 1, "linear", "")
+
+	# Create the logical system.
+	call mw_newsystem (mw, "logical", ndim)
+	do i = 1, ndim
+	    call mw_swtype (mw, i, 1, "linear", "")
+
+	# Set W and CD for the logical system to point to the Lterm.
+	wp = MI_WCS(mw)
+	WCS_W(wp) = MI_LTV(mw)
+	WCS_CD(wp) = MI_LTM(mw)
+
+	# Set the default world system.
+	call mw_sdefwcs (mw)
+
+	return (mw)
+end