Question

我正在TensorFlow中进行基本的轨道力学仿真。当“行星”太靠近“太阳”时（当x，y接近（0,0）时），TensorFlow在除法过程中会获得异常（这可能是有道理的）。它以某种方式在异常期间返回异常，导致其完全失败。

我尝试使用tf.where有条件地将这些除数用NaN替换为零，但是实际上它遇到了相同的错误。我还尝试过使用tf.div_no_nan而不是NaN来获得零，但这会得到完全相同的错误。

import tensorflow as tf
import numpy as np
import matplotlib.pyplot as plt

def gravity(state, t):
    print(len(tf.unstack(state)))
    x, y, vx, vy = tf.unstack(state)
    # Error is related to next two lines
    fx = -x/tf.pow(tf.reduce_sum(tf.square([x,y]),axis=0),3/2)
    fy = -y/tf.pow(tf.reduce_sum(tf.square([x,y]),axis=0),3/2)
    dvx = fx
    dvy = fy
    return tf.stack([vx, vy, dvx, dvy])

# Num simulations
size = 100

# Initialize at same position with varying y-velocity
init_state = tf.stack([tf.constant(-1.0,shape=(size,)),tf.zeros((size)),tf.zeros((size)),tf.range(0,10,.1)])

t = np.linspace(0, 10, num=5000)
tensor_state, tensor_info = tf.contrib.integrate.odeint(
    gravity, init_state, t, full_output=True)

init = tf.global_variables_initializer()
with tf.Session() as sess:   
    state, info = sess.run([tensor_state, tensor_info])
    state = tf.transpose(state, perm=[1,2,0]).eval()

x, y, vx, vy = state
for i in range(10):
    plt.figure()
    plt.plot(x[i], y[i])
    plt.scatter([0],[0])

我实际上得到了

...
InvalidArgumentError: assertion failed: [underflow in dt] [9.0294095248318226e-17]
...
During handling of the above exception, another exception occurred:
...
InvalidArgumentError: assertion failed: [underflow in dt] [9.0294095248318226e-17]
...

我希望除法结果为NaN或无穷大，然后像通常期望的那样对数值积分进行传播。

Answer 1

您可以尝试

with tf.Session() as sess:
    sess.run(init)
    try:
        state, info = sess.run([tensor_state, tensor_info])
    except tf.errors.InvalidArgumentError:
        state = #Whatever values/shape you need

我不知道这是否适合您的情况，但也许您可以添加一些小常数以避免被零除。

数值积分过程中的异常处理异常

1 个答案: