'Set the sizes of each member of the collection.
Parameters
sizes : ndarray or None
The size to set for each element of the collection.  The
value is the \'area\' of the element.
dpi : float
The dpi of the canvas. Defaults to 72.0.'

def set_sizes(self, sizes, dpi=72.0):

    if (sizes is None):
        self._sizes = np.array([])
        self._transforms = np.empty((0, 3, 3))
    else:
        self._sizes = np.asarray(sizes)
        self._transforms = np.zeros((len(self._sizes), 3, 3))
        scale = (((np.sqrt(self._sizes) * dpi) / 72.0) * self._factor)
        self._transforms[:, 0, 0] = scale
        self._transforms[:, 1, 1] = scale
        self._transforms[:, 2, 2] = 1.0
    self.stale = True
