boston                  Boston Housing Data
ppm                     Penalized Principal Machine for Sufficient
                        Dimension Reduction
ppm_tune                Cross-Validation for the Penalized Principal
                        Machine Tuning Parameter
print.ppm               Print a fitted penalized principal machine
print.ppm_tune          Print a penalized principal machine
                        cross-validation result
summary.ppm             Summarize a fitted penalized principal machine
wdbc                    Wisconsin Diagnostic Breast Cancer (WDBC) Data
