建立Tensor

目錄

• 建立Tensor
• numpy, list
  • numpy
  • list
• zeros, ones, fill
  • zeros
  • ones
  • fill
• random
  • 打亂idx後，a和b的索引不變
• constant
• loss計算
  • 無bias的loss

建立Tensor

* from numpy, list
* zeros, ones, fill
* random  # if big dimension, random initial
* constant
* Application

numpy, list

numpy

import numpy as np
import tensorflow as tf

tf.convert_to_tensor(np.ones([2, 3]))

<tf.Tensor: id=0, shape=(2, 3), dtype=float64, numpy=
array([[1., 1., 1.],
       [1., 1., 1.]])>

tf.convert_to_tensor(np.zeros([2, 3]))

<tf.Tensor: id=2, shape=(2, 3), dtype=float64, numpy=
array([[0., 0., 0.],
       [0., 0., 0.]])>

list

tf.convert_to_tensor([1, 2])

<tf.Tensor: id=4, shape=(2,), dtype=int32, numpy=array([1, 2], dtype=int32)>

tf.convert_to_tensor([1, 2.])

<tf.Tensor: id=6, shape=(2,), dtype=float32, numpy=array([1., 2.], dtype=float32)>

tf.convert_to_tensor([[1], [2.]])

<tf.Tensor: id=8, shape=(2, 1), dtype=float32, numpy=
array([[1.],
       [2.]], dtype=float32)>

zeros, ones, fill

zeros

tf.zeros([])

<tf.Tensor: id=10, shape=(), dtype=float32, numpy=0.0>

tf.zeros([1])

<tf.Tensor: id=14, shape=(1,), dtype=float32, numpy=array([0.], dtype=float32)>

tf.zeros([2, 2])

<tf.Tensor: id=18, shape=(2, 2), dtype=float32, numpy=
array([[0., 0.],
       [0., 0.]], dtype=float32)>

tf.zeros([2, 3, 3])

<tf.Tensor: id=22, shape=(2, 3, 3), dtype=float32, numpy=
array([[[0., 0., 0.],
        [0., 0., 0.],
        [0., 0., 0.]],

       [[0., 0., 0.],
        [0., 0., 0.],
        [0., 0., 0.]]], dtype=float32)>

a = tf.constant([0])
tf.zeros_like(a)  # 等同於tf.zeros(a.shape)

<tf.Tensor: id=25, shape=(1,), dtype=int32, numpy=array([0], dtype=int32)>

ones

tf.ones(1)

<tf.Tensor: id=29, shape=(1,), dtype=float32, numpy=array([1.], dtype=float32)>

tf.ones([])

<tf.Tensor: id=31, shape=(), dtype=float32, numpy=1.0>

tf.ones([2])

<tf.Tensor: id=35, shape=(2,), dtype=float32, numpy=array([1., 1.], dtype=float32)>

tf.ones([2, 3])

<tf.Tensor: id=39, shape=(2, 3), dtype=float32, numpy=
array([[1., 1., 1.],
       [1., 1., 1.]], dtype=float32)>

a = tf.constant([0])
tf.ones_like(a)  # # 等同於tf.ones(a.shape)

<tf.Tensor: id=44, shape=(1,), dtype=int32, numpy=array([1], dtype=int32)>

fill

tf.fill([2, 2], 0)

<tf.Tensor: id=48, shape=(2, 2), dtype=int32, numpy=
array([[0, 0],
       [0, 0]], dtype=int32)>

tf.fill([2, 2], 0)

<tf.Tensor: id=52, shape=(2, 2), dtype=int32, numpy=
array([[0, 0],
       [0, 0]], dtype=int32)>

tf.fill([2, 2], 1)

<tf.Tensor: id=56, shape=(2, 2), dtype=int32, numpy=
array([[1, 1],
       [1, 1]], dtype=int32)>

tf.fill([2, 2], 9)

<tf.Tensor: id=60, shape=(2, 2), dtype=int32, numpy=
array([[9, 9],
       [9, 9]], dtype=int32)>

random

# 正態分佈，均值爲1，方差爲1
tf.random.normal([2, 2], mean=1, stddev=1)

<tf.Tensor: id=67, shape=(2, 2), dtype=float32, numpy=
array([[1.0804566, 0.9318387],
       [1.0620257, 0.6907253]], dtype=float32)>

tf.random.normal([2, 2])

<tf.Tensor: id=74, shape=(2, 2), dtype=float32, numpy=
array([[-0.06452972,  0.05704789],
       [ 0.82857376,  0.71619517]], dtype=float32)>

# 截斷的正態分佈，
tf.random.truncated_normal([2, 2], mean=0, stddev=1)

<tf.Tensor: id=81, shape=(2, 2), dtype=float32, numpy=
array([[ 0.19161457, -0.820383  ],
       [ 0.43668088, -0.3798696 ]], dtype=float32)>

以下圖所示爲截斷正態分佈，截掉紅色部分，對新的正態分佈從新採樣。由於sigmoid的和新的正態分佈不衝突的地方的區域，對於sigmoid函數來講是近似於平滑的直線，梯度爲0，所以會有梯度消失。

# 均勻分佈
tf.random.uniform([2, 2], minval=0, maxval=1)

<tf.Tensor: id=89, shape=(2, 2), dtype=float32, numpy=
array([[0.01481438, 0.15071952],
       [0.5599004 , 0.59821343]], dtype=float32)>

tf.random.uniform([2, 2], minval=0, maxval=100, dtype=tf.int32)

<tf.Tensor: id=102, shape=(2, 2), dtype=int32, numpy=
array([[51,  9],
       [10, 14]], dtype=int32)>

打亂idx後，a和b的索引不變

idx = tf.range(10)
idx = tf.random.shuffle(idx)
idx

<tf.Tensor: id=113, shape=(10,), dtype=int32, numpy=array([0, 8, 4, 9, 6, 7, 5, 2, 1, 3], dtype=int32)>

a = tf.random.normal([10, 784])
b = tf.random.uniform([10], maxval=10, dtype=tf.int32)
b

<tf.Tensor: id=134, shape=(10,), dtype=int32, numpy=array([1, 8, 1, 2, 4, 6, 2, 7, 4, 5], dtype=int32)>

a = tf.gather(a, idx)
b = tf.gather(b, idx)
b

<tf.Tensor: id=147, shape=(10,), dtype=int32, numpy=array([1, 8, 2, 2, 6, 1, 7, 4, 4, 5], dtype=int32)>

constant

tf.constant(1)

<tf.Tensor: id=149, shape=(), dtype=int32, numpy=1>

tf.constant([1])

<tf.Tensor: id=151, shape=(1,), dtype=int32, numpy=array([1], dtype=int32)>

tf.constant([1, 2.])

<tf.Tensor: id=153, shape=(2,), dtype=float32, numpy=array([1., 2.], dtype=float32)>

tf.constant([[1, 2], [3., 2]])

<tf.Tensor: id=156, shape=(2, 2), dtype=float32, numpy=
array([[1., 2.],
       [3., 2.]], dtype=float32)>

loss計算

無bias的loss

out = tf.random.uniform([4, 10])
out

<tf.Tensor: id=171, shape=(4, 10), dtype=float32, numpy=
array([[0.67733276, 0.2267617 , 0.21761227, 0.28679788, 0.68864655,
        0.21349418, 0.5646602 , 0.8294822 , 0.22094071, 0.20246148],
       [0.7940483 , 0.86402774, 0.78399694, 0.80085063, 0.01357341,
        0.11889946, 0.89162886, 0.755934  , 0.8058628 , 0.40188062],
       [0.115659  , 0.30951428, 0.39866602, 0.5358803 , 0.9163326 ,
        0.47557557, 0.9397205 , 0.3110628 , 0.49839914, 0.34321547],
       [0.5563061 , 0.78829396, 0.52705276, 0.29077685, 0.35033226,
        0.9630101 , 0.338771  , 0.6301584 , 0.7393383 , 0.7073529 ]],
      dtype=float32)>

y = tf.range(4)
y = tf.one_hot(y, depth=10)
y

<tf.Tensor: id=188, shape=(4, 10), dtype=float32, numpy=
array([[1., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 1., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 1., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 1., 0., 0., 0., 0., 0., 0.]], dtype=float32)>

loss = tf.keras.losses.mse(y, out)
loss

<tf.Tensor: id=195, shape=(4,), dtype=float32, numpy=array([0.19016443, 0.4096697 , 0.31698173, 0.43206215], dtype=float32)>

loss = tf.reduce_mean(loss)
loss

<tf.Tensor: id=200, shape=(), dtype=float32, numpy=0.3372195>