Couldn't generate code for the following reason:
Encountered unsupported operator partialdiff; 
  In MathML apply element with ID membrane_voltage_partialdiff_eq.
  In MathML math element.
  In CellMLComponent element with name membrane.
  In Model element with cmeta:id surkis_peskin_tranchina_leonard_1998_version01 with name surkis_peskin_tranchina_leonard_1998_version01.