perldl> ?? inverse
PDL::Transform::unmap ...
                Map an image or N-D dataset using the inverse as a
                coordinate transform.
erfi            The inverse of the error function. Works inplace.
ifft            Complex Inverse FFT of the "real" and "imag" arrays
                [inplace]
ifftnd          N-dimensional inverse FFT
invert          Apply an inverse transformation to some input
                coordinates.
realifft        Inverse of one-dimensional realfft routine [inplace].
t_fits          FITS pixel-to-scientific transformation with inverse
t_inverse    Return the inverse of a PDL::Transform. This just
                reverses the func/inv, idim/odim, itype/otype, and
                iunit/ounit pairs. Note that sometimes you end up
                with a transform that cannot be applied or mapped,
                because either the mathematical inverse doesn't exist
                or the inverse func isn't implemented.
t_quadratic     Quadratic scaling -- cylindrical pincushion
                      (n-d; with inverse)
t_radial        Convert Cartesian to radial/cylindrical coordinates.
                      (2-D/3-D; with inverse)
t_spherical     Convert Cartesian to spherical coordinates.
                      (3-D; with inverse)