Returns a list of points for a piece-wise linear function from the
        given offer/bid blocks.

def _offbids_to_points(self, offbids, arebids=False):
        """ Returns a list of points for a piece-wise linear function from the
        given offer/bid blocks.
        """
        # Sort offers/bids by price in ascending order.
        offbids.sort(key=lambda x: x.price, reverse=arebids)

        points = [(0.0, offbids[0].noLoadCost)]
        # Form piece-wise linear total cost function.
        for i, offbid in enumerate(offbids):
            x1, y1 = points[i]
            x2 = x1 + offbid.quantity # MW.
            m = offbid.price # $/MWh
            y2 = m * (x2 - x1) + y1
            points.append((x2, y2))

        if arebids:
            points = [(-x, -y) for x, y in points]
            points.reverse()

#        n_segs = len(points) - 1
#        logger.info("%d segment pwl cost function: %s" % (n_segs, points))

        return points