type error when calculating distributions

[ethanagb]

Traceback (most recent call last):
  File "../v1/simulation.py", line 170, in <module>
    simulateReads(sys.argv[1:])
  File "../v1/simulation.py", line 84, in simulateReads
    mu = np.log(mean)-0.5*sigma**2
TypeError: ufunc 'log' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''