e iterations) at each
        cycle iteration.
    For more detail, please see paper.

    # Example
        ```python
            clr = CyclicLR(base_lr=0.001, max_lr=0.006,
                                step_size=2000., mode=&#39;triangular&#39;)
            model.fit(X_train, Y_train, callbacks=[clr])
        ```

    Class also supports custom scaling functions:
        ```python
            clr_fn = lambda x: 0.5*(1+np.sin(x*np.pi/2.))
            clr = CyclicLR(base_lr=0.001, max_lr=0.006,
         