def partTypeNum(partType):
    """ Mapping between common names and numeric particle types. """
    if str(partType).isdigit():
        return int(partType)
    
    if str(partType).lower() in ['gas','cells']:
        return 0
    if str(partType).lower() in ['dm','darkmatter']:
        return 1
    if str(partType).lower() in ['tracer','tracers','tracermc','trmc']:
        return 3
    if str(partType).lower() in ['star','stars','stellar']:
        return 4 # only those with GFM_StellarFormationTime>0
    if str(partType).lower() in ['wind']:
        return 4 # only those with GFM_StellarFormationTime<0
    if str(partType).lower() in ['bh','bhs','blackhole','blackholes']:
        return 5
    
    raise Exception("Unknown particle type name.")