Hello, I’m new to yt so this maybe solved easily, though it puzzled me for quite some time and I still don’t understand what is going on. I try to create derived fields to analyze a simulation using AMR, from an output from CHOMBO. I define the following derived fields: def _VRA(field,data): return data['Cylsin']*data['Vx2'] def _VRB(field,data): return data['Cylcos']*data['Vx1'] def _VVR(field,data): return data['VRA']+data['VRB'] Then I add them to my yt object: ds=yt.load(file) ds.index ds.add_field(('chombo','VRA'),function=_VRA,units='cm/s',take_log=False) ds.add_field(('chombo','VRB'),function=_VRB,units='cm/s',take_log=False) ds.add_field(('chombo','VVR'),function=_VVR,units='cm/s',take_log=False) and everything goes on smoothly (they are the only variables named this way). Now, If I try to slice VRA and VRB I obtain the (correct) attached plots. Both VRA and VRB are strictly positive. If I try to slice VVR which is the sum VRA+VRB, I obtained the third attached plot which does not correspond to the expected sum (there are even negative values)! I suspect something went odd in the slice function, but I used the exact same lines of code to generate the three plots. I must be missing something here but I really don’t get it. Many thanks in advance for your help! Antoine Antoine STRUGAREK ------------------------------------------------------------------- Webpage Département de physique, Université de Montréal strugarek@astro.umontreal.ca (+1) 514 343 7077 -------------------------------------------------------------------- DSM/IRFU/SAp/LDEE CEA Saclay DSM/IRFM/SCCP CEA Cadarache antoine.strugarek@cea.fr --------------------------------------------------------------------
