Traceback (most recent call last):
  File "pvmismatch\contrib\gen_coeffs\tests\test_two_diode.py", line 63, in test_didv_dpdv_frsh
    fdidv_expected = np.float(didv_simple.evalf(subs=expected_data))
  File "python27\lib\site-packages\sympy\core\expr.py", line 239, in __float__
    raise TypeError("can't convert expression to float")
TypeError: can't convert expression to float