Should coordmap composition check coordinate system names?

[matthew-brett]

At the moment, this gives an error:

import numpy as np

from nipy.core.api import CoordinateSystem, AffineTransform, compose

ijk = CoordinateSystem('ijk', 'voxel')
xyz = CoordinateSystem('xyz', 'world')
ijk_to_xyz = AffineTransform(ijk, xyz, np.eye(4))

pqr = CoordinateSystem('pqr', 'crazy')
ijk2 = CoordinateSystem('ijk', 'another_name')
pqr_to_ijk = AffineTransform(pqr, ijk2, np.eye(4))

pqr_to_xyz = compose(ijk_to_xyz, pqr_to_ijk)

The error is:

ValueError                                Traceback (most recent call last)
<ipython-input-23-42effb708f95> in <module>()
----> 1 pqr_to_xyz = compose(ijk_to_xyz, pqr_to_ijk)

/Users/mb312/usr/local/lib/python2.6/site-packages/nipy/core/reference/coordinate_map.pyc in compose(*cmaps)
1085     allaffine = np.all([isinstance(cmap, AffineTransform) for cmap in cmaps])
1086     if allaffine:
-> 1087         return _compose_affines(*cmaps)
1088     else:
1089         warnings.warn("composition of non-affine CoordinateMaps is "

/Users/mb312/usr/local/lib/python2.6/site-packages/nipy/core/reference/coordinate_map.pyc in _compose_affines(*affines)
1584                                   np.dot(cmap.affine, cur.affine))
1585         else:
-> 1586             raise ValueError("domains and ranges don't match up correctly")
1587     return cur
1588 

ValueError: domains and ranges don't match up correctly

That is because the 'ijk' and 'ijk2' coordinate systems have the same axis names, but different coordinate names. I think we should probably only check the coordinate axis names, not the coordinate system name....