如何在Keras中实现RBF激活函数？

import keras.backend as K
from keras.layers import Layer

class RBF(Layer):
    def __init__(self, units, **kwargs):
        self.units = units
        super(RBF, self).__init__(**kwargs)

    def build(self, input_shape):
        self.centers = self.add_weight(name='centers',
                                       shape=(self.units, input_shape[1]),
                                       initializer='uniform',
                                       trainable=True)
        super(RBF, self).build(input_shape)

    def call(self, inputs):
        diff = K.expand_dims(inputs) - self.centers
        dist = K.sum(K.square(diff), axis=2)
        return K.exp(-0.1 * dist)

    def compute_output_shape(self, input_shape):
        return input_shape[0], self.units

from keras.models import Sequential
from keras.layers import Dense

model = Sequential()
model.add(Dense(64, input_dim=100))
model.add(RBF(10))