add the following codes to allocate a GPU to your codes:

>>>import tensorflow as tf
>>>from keras.backend.tensorflow_backend import set_session

>>>np.set_printoptions(suppress=True)
>>>os.environ["CUDA_VISIBLE_DEVICES"]="0"
>>>config = tf.ConfigProto()
>>>config.gpu_options.per_process_gpu_memory_fraction = 0.95
>>>set_session(tf.Session(config=config))