'Return definite integral of the spline between two given points.
Parameters
a : float
Lower limit of integration.
b : float
Upper limit of integration.
Returns
integral : float
The value of the definite integral of the spline between limits.
Examples
>>> from scipy.interpolate import UnivariateSpline
>>> x = np.linspace(0, 3, 11)
>>> y = x**2
>>> spl = UnivariateSpline(x, y)
>>> spl.integral(0, 3)
9.0
which agrees with :math:`\int x^2 dx = x^3 / 3` between the limits
of 0 and 3.
A caveat is that this routine assumes the spline to be zero outside of
the data limits:
>>> spl.integral(-1, 4)
9.0
>>> spl.integral(-1, 0)
0.0'

def integral(self, a, b):

    return dfitpack.splint(*(self._eval_args + (a, b)))
