ctc_cost.py 文件源码

def stable_softmax(y_hat):
    """Calculate softmax and log softmax in numerically stable way

    Parameters
    ----------
    y_hat : tensor3 (input_seq_len, num_batch, num_classes+1)
        class energies

    Return
    ------
    softmax values in normal and log domain
    """
    y_hat_safe = y_hat - y_hat.max(axis=2, keepdims=True)
    y_hat_safe_exp = T.exp(y_hat_safe)
    y_hat_safe_normalizer = y_hat_safe_exp.sum(axis=2, keepdims=True)
    log_y_hat_safe_normalizer = T.log(y_hat_safe_normalizer)

    y_hat_softmax = y_hat_safe_exp / y_hat_safe_normalizer
    log_y_hat_softmax = y_hat_safe - log_y_hat_safe_normalizer

    return y_hat_softmax, log_y_hat_softmax