<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _pdf_w_mean(self, x, mean, sigma):
 """ Calculates the pdf of a lognormal distribution with parameters mean and sigma Parameters mean : float or ndarray Mean of the lognormal distribution sigma : float or ndarray Sigma parameter of the lognormal distribution Returns ------- : float or ndarray pdf of x """


        # Lognorm pmf with mean for optimization
        mu, sigma = self.translate_args(mean, sigma)
        return self.logpdf(x, mu, sigma)