How do I search for a function?

Use the PerlDL shell (either pdl2 or perldl) on your computer. For example, use the help command to learn about xvals:

pdl> help xvals

If you don't know the exact name of the function, use the apropos command to do a fuzzy seach:

pdl> apropos xval
mn_init         The function mn_init() does the basic initialization of the
                fit. The first argument has to be a reference to the function
                to be minimized.
xlinvals        X axis values between endpoints (see xvals).
xlogvals        X axis values logarithmicly spaced between endpoints (see xvals).
xvals           Fills a piddle with X index values. Uses similar specifications
                to zeroes and new_from_specification.
yvals           Fills a piddle with Y index values. See the CAVEAT for xvals.
zvals           Fills a piddle with Z index values. See the CAVEAT for xvals.

The apropos command does a regex search for function names and descriptions.