def bottom(x): # Triangular island with pit on right slope
        H = 10.0
        island_height = 20.0
        island_half_width = 222
        pit_offset = 120.0
        pit_halfwidth = 50.0
        pit_depth = 6.0
        xc = (x[0] + x[-1]) / 2
        distance = np.abs(x - xc)
        b = np.zeros_like(x)
        mask = distance <= island_half_width
        b[mask] = island_height * (1 - distance[mask] / island_half_width)
        pit_center = xc + pit_offset # pit on right slope
        d = np.abs(x - pit_center)
        pit_mask = (x > xc) & (d <= pit_halfwidth)
        b[pit_mask] -= pit_depth * (1 - d[pit_mask] / pit_halfwidth)
        return -(H - b)