第一次运行可以出结果，再运行就报错

import paddle.fluid as fluid
import numpy
#定义数据
train_data=numpy.array([[1.0],[2.0],[3.0],[4.0]]).astype('float32')
y_true = numpy.array([[2.0],[4.0],[6.0],[8.0]]).astype('float32')
#定义网络
a = fluid.layers.data(name="a",shape=[1],dtype='float32')
y = fluid.layers.data(name="y",shape=[1],dtype='float32')
y_predict = fluid.layers.fc(input=a,size=1,act=None)
#定义损失函数
cost = fluid.layers.square_error_cost(input=y_predict,label=y)
avg_cost = fluid.layers.mean(cost)
#定义优化方法
sgd_optimizer = fluid.optimizer.SGD(learning_rate=0.01)
sgd_optimizer.minimize(avg_cost)
#参数初始化
cpu = fluid.core.CPUPlace()
exe = fluid.Executor(cpu)
exe.run(fluid.default_startup_program())
##开始训练，迭代100次
for i in range(100):
    outs = exe.run(
        feed={'a':train_data,'y':y_true},
        fetch_list=[y_predict.name,avg_cost.name])
#观察结果
print(outs)

错误提示

EnforceNotMet: Invoke operator mul error.
Python Callstacks: 
  File "d:\ProgramData\Anaconda3\lib\site-packages\paddle\fluid\framework.py", line 1317, in append_op
    attrs=kwargs.get("attrs", None))
  File "d:\ProgramData\Anaconda3\lib\site-packages\paddle\fluid\layer_helper.py", line 56, in append_op
    return self.main_program.current_block().append_op(*args, **kwargs)
  File "d:\ProgramData\Anaconda3\lib\site-packages\paddle\fluid\layers\nn.py", line 284, in fc
    "y_num_col_dims": 1})
  File "F:/研究生资料/paddle/官方入门例子.py", line 20, in 
    y_predict = fluid.layers.fc(input=x,size=1,act=None)
  File "d:\ProgramData\Anaconda3\lib\site-packages\spyder\utils\site\sitecustomize.py", line 102, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)
  File "d:\ProgramData\Anaconda3\lib\site-packages\spyder\utils\site\sitecustomize.py", line 705, in runfile
    execfile(filename, namespace)
  File "", line 1, in 
    runfile('F:/研究生资料/paddle/官方入门例子.py', wdir='F:/研究生资料/paddle')
  File "d:\ProgramData\Anaconda3\lib\site-packages\IPython\core\interactiveshell.py", line 2910, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "d:\ProgramData\Anaconda3\lib\site-packages\IPython\core\interactiveshell.py", line 2856, in run_ast_nodes
    if self.run_code(code, result):
  File "d:\ProgramData\Anaconda3\lib\site-packages\IPython\core\interactiveshell.py", line 2728, in run_cell
    interactivity=interactivity, compiler=compiler, result=result)
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\zmqshell.py", line 537, in run_cell
    return super(ZMQInteractiveShell, self).run_cell(*args, **kwargs)
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\ipkernel.py", line 208, in do_execute
    res = shell.run_cell(code, store_history=store_history, silent=silent)
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", line 399, in execute_request
    user_expressions, allow_stdin)
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", line 233, in dispatch_shell
    handler(stream, idents, msg)
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", line 283, in dispatcher
    return self.dispatch_shell(stream, msg)
  File "d:\ProgramData\Anaconda3\lib\site-packages\tornado\stack_context.py", line 277, in null_wrapper
    return fn(*args, **kwargs)
  File "d:\ProgramData\Anaconda3\lib\site-packages\zmq\eventloop\zmqstream.py", line 414, in _run_callback
    callback(*args, **kwargs)
  File "d:\ProgramData\Anaconda3\lib\site-packages\zmq\eventloop\zmqstream.py", line 472, in _handle_recv
    self._run_callback(callback, msg)
  File "d:\ProgramData\Anaconda3\lib\site-packages\zmq\eventloop\zmqstream.py", line 352, in flush
    self._handle_recv()
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", line 298, in do_one_iteration
    stream.flush(zmq.POLLIN, 1)
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\eventloops.py", line 39, in process_stream_events
    kernel.do_one_iteration()
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\eventloops.py", line 95, in _loop_qt
    app.exec_()
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\eventloops.py", line 111, in loop_qt4
    _loop_qt(kernel.app)
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\eventloops.py", line 123, in loop_qt5
    return loop_qt4(kernel)
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", line 263, in enter_eventloop
    self.eventloop(self)
  File "d:\ProgramData\Anaconda3\lib\site-packages\tornado\stack_context.py", line 277, in null_wrapper
    return fn(*args, **kwargs)
  File "d:\ProgramData\Anaconda3\lib\site-packages\tornado\ioloop.py", line 605, in _run_callback
    ret = callback()
  File "d:\ProgramData\Anaconda3\lib\site-packages\tornado\ioloop.py", line 832, in start
    self._run_callback(self._callbacks.popleft())
  File "d:\ProgramData\Anaconda3\lib\site-packages\zmq\eventloop\ioloop.py", line 177, in start
    super(ZMQIOLoop, self).start()
  File "d:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelapp.py", line 478, in start
    self.io_loop.start()
  File "d:\ProgramData\Anaconda3\lib\site-packages\spyder\utils\ipython\start_kernel.py", line 264, in main
    kernel.start()
  File "d:\ProgramData\Anaconda3\lib\site-packages\spyder\utils\ipython\start_kernel.py", line 268, in 
    main()
C++ Callstacks: 
Input X(0)is not initialized at [D:\1.3\paddle\paddle\fluid\framework\operator.cc:1093]
PaddlePaddle Call Stacks: 
Windows not support stack backtrace yet.