Hi all, I was trying to calculate the spin parameter for a halo with the following simple script, center = [0.495013, 0.494046, 0.495160] radius = 100 # pc pf = load("DD0019/output_0019") sp = pf.h.sphere(center, radius/pf["pc"]) gas_spin = sp.quantities["BaryonSpinParameter"]() and it doesn't work in parallel. It gives the following traceback. --- Traceback (most recent call last): File "spin.py", line 9, in <module> gas_spin = sp.quantities["BaryonSpinParameter"]() File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/yt-2.1dev-py2.6-macosx-10.6-intel.egg/yt/data_objects/derived_quantities.py", line 85, in __call__ self.func(e, *args, **kwargs) File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/yt-2.1dev-py2.6-macosx-10.6-intel.egg/yt/data_objects/derived_quantities.py", line 237, in _BaryonSpinParameter am = data["SpecificAngularMomentum"]*data["CellMassMsun"] ValueError: shape mismatch: objects cannot be broadcast to a single shape Traceback (most recent call last): File "spin.py", line 9, in <module> gas_spin = sp.quantities["BaryonSpinParameter"]() File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/yt-2.1dev-py2.6-macosx-10.6-intel.egg/yt/data_objects/derived_quantities.py", line 85, in __call__ self.func(e, *args, **kwargs) File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/yt-2.1dev-py2.6-macosx-10.6-intel.egg/yt/data_objects/derived_quantities.py", line 237, in _BaryonSpinParameter am = data["SpecificAngularMomentum"]*data["CellMassMsun"] ValueError: shape mismatch: objects cannot be broadcast to a single shape --- This happens on multiple systems. I looked into this further, and I think the shapes of the angular momentum data are not being preserved in the MPI calls. Also the shapes appear wrong in a serial calculation. In serial, everything looks fine until data["SpecificAngularMomentum"] is returned. Here are the shapes of the arrays. v_vec: (3,16,16,16) cross product of r_vec and v_vec: (3,16,16,16) and the returned array from _SpecificAngularMomentum has a shape of (3,0)! Then when I try to run it with 2 processors, the shapes change to v_vec: (3,4096) cross: (3,4096) _SpecificAngularMomentum result: (12288,) Can someone replicate this error? Any ideas? Thanks, John