Dear yt people, I am working on a tipsy output file from a n-body simulation. My file contains some scaled units for fields like density, coordinates, mass etc. To make a physical sense of the data, I had to convert those fields units to some physical units (c.g.s) and I derived new fields having cgs unit. for example: *dd = ds.all_data()# derive a new domain width with conversion factor (6Mpc*current_time/hubble_constant) def _NewDomainWidth(field, data): return ds.domain_width*((3.086e18*6e6*0.909090893796)/(0.7))ds.add_field(('gas', 'PhysicalDomainWidth'), function=_NewDomainWidth, units="code_length")* *# derive a new domain center with conversion factor (6Mpc*current_time/hubble_constant) def _NewDomainCenter(field, data): return ds.domain_center*((3.086e18*6e6*0.909090893796)/(0.7))ds.add_field(('gas', 'PhysicalDomainCenter'), function=_NewDomainCenter, units="code_length")* note that here "code_length" is actually in "cm". but I could not just do dd["Gas",'Coordinates'].in_units('cm'), because this conversion does not take into account some constant corrections and returns the wrong length magnitude. My goal was to make sliceplot and projectionplot of a newly derived field : *# derive a new electron pressure fielddef _ElectronPressure(field, data): return data['Gas','Density']*(5.49e-7)*data['Gas','Temperature']ds.add_field(('gas', 'ElectronPressure'), function=_ElectronPressure, units="(code_mass*K)/(code_length**3)")* *# integration of pressure field along line of sight* *yt.ProjectionPlot(ds, 'z', ('gas', 'ElectronPressure'), width = dd['gas', 'PhysicalDomainWidth'], center = dd['gas', 'PhysicalDomainCenter'] )* *and it is returning me * ValueError Traceback (most recent call last)<ipython-input-8-fa351b6c09d1> in <module>() 1 yt.ProjectionPlot(ds, 'z', ('gas', 'ElectronPressure'), width = dd['gas', 'PhysicalDomainWidth'], ----> 2 center = dd['gas', 'PhysicalDomainCenter'] ) ValueError: operands could not be broadcast together with shapes (39678,) (54608,) Now I cannot use width =ds.domain_width and center = ds.domain_center for the same unit error. I was wondering how I can make the projectionplot for my newly derived field and newly derived domain width and domain center. Your suggestion is most welcome Best Tazkera