def _call(self, x, out=None):
        """Apply resampling operator.

        The element ``x`` is resampled using the sampling and interpolation
        operators of the underlying spaces.
        """
        if out is None:
            return x.interpolation
        else:
            out.sampling(x.interpolation)
Apply resampling operator.

        The element ``x`` is resampled using the sampling and interpolation
        operators of the underlying spaces.