statsmodels/statsmodels — comment on commit 17540867ef660d39bc19e15526adcf342ff2c44b
File:  line 0
By josef-pkt:

to hessian, cs (norm.cdf not for complex) and approx3 (bug) don't work, the following seems to work, I get valid bse for all estimators

```
def hessian(self, params):
loglike = self.loglike
#return approx_hess(params, loglike, epsilon=1e-4)[0]
plus = approx_hess(params, loglike, epsilon=1e-4)[0]
minus = approx_hess(params, loglike, epsilon=-1e-4)[0]
return 0.5 * (plus + minus)
```

I had used this before (I hope I remember correctly) to get central difference hessian out of the forward only