def PrefixNotation(significand, prefix=''):
    """significand -> float
prefix  -> str
return the corresponding decimal number -> float

prefix is one of :
'p' pico, 'n', 'u' or 'µ' micro, 'm', 'k', 'M' mega, 'G', 'T', '' default

>>> from dcelectricity import dc_en as dc
>>> dc.PrefixNotation(20, 'm')  # 0.02
>>> dc.PrefixNotation(50, 'k')  # 50000
>>> dc.PrefixNotation(-10000)   # -10000
"""
    prefixes = {'': 1, 'p': 1e-12, 'n': 1e-09, 'u': 1e-06, 'µ': 1e-06, 'm':
        0.001, 'k': 1000.0, 'M': 1000000.0, 'G': 1000000000.0, 'T': 
        1000000000000.0}
    return significand * prefixes[prefix]
