@pimms.calc('<STR_LIT>')<EOL>def calc_model(cortex, model_argument, model_hemi=Ellipsis, radius=np.pi/<NUM_LIT:3>):
if pimms.is_str(model_argument):<EOL><INDENT>h = cortex.chirality if model_hemi is Ellipsis elseNone             if model_hemi is None     elsemodel_hemi<EOL>model = retinotopy_model(model_argument, hemi=h, radius=radius)<EOL><DEDENT>else:<EOL><INDENT>model = model_argument<EOL><DEDENT>if not isinstance(model, RegisteredRetinotopyModel):<EOL><INDENT>raise ValueError('<STR_LIT>')<EOL><DEDENT>return model<EOL>
calc_model loads the appropriate model object given the model argument, which may given the name
of the model or a model object itself.

Required afferent parameters:
  @ model_argument Must be either a RegisteredRetinotopyModel object or the name of a model that
    can be loaded.

Optional afferent parameters:
  @ model_hemi May be used to specify the hemisphere of the model; this is usually only used
    when the fsaverage_sym hemisphere is desired, in which case this should be set to None; if
    left at the default value (Ellipsis), then it will use the hemisphere of the cortex param.

Provided efferent values:
  @ model Will be the RegisteredRetinotopyModel object to which the mesh should be registered.