# scipy.stats.boxcox_normplot

scipy.stats.boxcox_normplot(x, la, lb, plot=None, N=80)

  Compute parameters for a Box-Cox normality plot, optionally show it.

  A Box-Cox normality plot shows graphically what the best transformation parameter is to use in `boxcox` to obtain a distribution that is close to normal.

  Parameters:
    x array_like

      Input array.

    la, lb scalar

      The lower and upper bounds for the `lmbda` values to pass to `boxcox` for Box-Cox transformations. These are also the limits of the horizontal axis of the plot if that is generated.

    plot object, optional

      If given, plots the quantiles and least squares fit. plot is an object that has to have methods “plot” and “text”. The `matplotlib.pyplot` module or a Matplotlib Axes object can be used, or a custom object with the same methods. Default is None, which means that no plot is created.

    N int, optional

      Number of points on the horizontal axis (equally distributed from la to lb).

  Returns:
    lmbdas ndarray

      The `lmbda` values for which a Box-Cox transform was done.

    ppcc ndarray

      Probability Plot Correlelation Coefficient, as obtained from `probplot` when fitting the Box-Cox transformed input x against a normal distribution.

  See also

  `probplot`, `boxcox`, `boxcox_normmax`, `boxcox_llf`, `ppcc_max`

  Notes

  Even if plot is given, the figure is not shown or saved by `boxcox_normplot`; `plt.show()` or `plt.savefig('figname.png')` should be used after calling `probplot`.

  Examples

      >>> from scipy import stats
      >>> import matplotlib.pyplot as plt

  Generate some non-normally distributed data, and create a Box-Cox plot:

      >>> x = stats.loggamma.rvs(5, size=500) + 5
      >>> fig = plt.figure()
      >>> ax = fig.add_subplot(111)
      >>> prob = stats.boxcox_normplot(x, -20, 20, plot=ax)

  Determine and plot the optimal `lmbda` to transform `x` and plot it in the same plot:

      >>> _, maxlog = stats.boxcox(x)
      >>> ax.axvline(maxlog, color='r')

      >>> plt.show()