1,2],[1,2]] represents ``1 + 1*x + 2*y + 2*x*y`` if axis=0 is
``x`` and axis=1 is ``y``.

Parameters
----------
c : array_like
    Array of polynomial coefficients. If c is multidimensional the
    different axis correspond to different variables with the degree
    in each axis given by the corresponding index.
m : int, optional
    Number of derivatives taken, must be non-negative. (Default: 1)
scl : scalar, optional
    Each differentiation is multiplied by `scl`.  The end result is
    multiplication by ``scl**m``.  This is for use in a linear change
    of variable. (Default: 1)
axis : int, optional
    Axis over which the derivative is taken. (Default: 0).

Returns
-------
der : ndarray
    Polynomial coefficients of the derivative.

See Also
--------
polyint

Examples
--------
>>> from numpy.polynomial import polynomial as P
>>> c = (1, 2, 3, 4)
>>> P.polyder(c)  # (d/dx)(c)
array([  2.,   6.,  12.])
>>> P.polyder(c, 3)  # (d**3/dx**3)(c)
array([24.])
>>> P.polyder(c, scl=-1)  # (d/d(-x))(c)
array([ -2.,  -6., -12.])
>>> P.polyder(c, 2, -1)  # (d**2/d(-x)**2)(c)
array([  6.,  24.])

r