electrostatics.py 文件源码

def fluxpoints(self, field, n, uniform=False):
        """Returns points where field lines should enter/exit the surface.

        The flux points are usually chosen so that they are equally separated
        in electric field flux.  However, if 'uniform' is True then the points
        are equispaced.

        This method requires that the flux be in xor out everywhere on the
        circle (unless 'uniform' is True)."""

        # Create a dense array of points around the circle
        a = radians(linspace(0, 360, 1001)) + self.a0
        assert len(a)%4 == 1
        x = self.r*array([cos(a), sin(a)]).T + self.x

        if uniform:
            flux = ones_like(a)

        else:
            # Get the flux through each point.  Ensure the fluxes are either
            # all in or all out.
            flux = field.projection(x, a)

            if numpy.sum(flux) < 0:
                flux *= -1
            assert alltrue(flux > 0)

        # Create an integrated flux curve
        intflux = insert(cumsum((flux[:-1]+flux[1:])/2), 0, 0)
        assert isclose(intflux[-1], numpy.sum(flux[:-1]))

        # Divide the integrated flux curve into n+1 portions, and calculate
        # the corresponding angles.
        v = linspace(0, intflux[-1], n+1)
        a = lininterp2(intflux, a, v)[:-1]

        return self.r*array([cos(a), sin(a)]).T + self.x