Warning: file_get_contents(/data/phpspider/zhask/data//catemap/4/json/15.json): failed to open stream: No such file or directory in /data/phpspider/zhask/libs/function.php on line 167

Warning: Invalid argument supplied for foreach() in /data/phpspider/zhask/libs/tag.function.php on line 1116

Notice: Undefined index: in /data/phpspider/zhask/libs/function.php on line 180

Warning: array_chunk() expects parameter 1 to be array, null given in /data/phpspider/zhask/libs/function.php on line 181
Python 为什么dot产品在斯坦福落后';s cs231n支持向量机?_Python_Math_Machine Learning_Deep Learning_Svm - Fatal编程技术网

Python 为什么dot产品在斯坦福落后';s cs231n支持向量机?

Python 为什么dot产品在斯坦福落后';s cs231n支持向量机?,python,math,machine-learning,deep-learning,svm,Python,Math,Machine Learning,Deep Learning,Svm,我正在看斯坦福大学cs231n的Youtube视频,并试图做练习。在执行SVM one时,我遇到了以下代码: def svm_loss_naive(W, X, y, reg): """ Structured SVM loss function, naive implementation (with loops). Inputs have dimension D, there are C classes, and we operate on minibatches of N ex

我正在看斯坦福大学cs231n的Youtube视频,并试图做练习。在执行SVM one时,我遇到了以下代码:

def svm_loss_naive(W, X, y, reg):
  """
  Structured SVM loss function, naive implementation (with loops).

  Inputs have dimension D, there are C classes, and we operate on minibatches
  of N examples.

  Inputs:
  - W: A numpy array of shape (D, C) containing weights.
  - X: A numpy array of shape (N, D) containing a minibatch of data.
  - y: A numpy array of shape (N,) containing training labels; y[i] = c means
    that X[i] has label c, where 0 <= c < C.
  - reg: (float) regularization strength

  Returns a tuple of:
  - loss as single float
  - gradient with respect to weights W; an array of same shape as W
  """
  dW = np.zeros(W.shape) # initialize the gradient as zero

  # compute the loss and the gradient
  num_classes = W.shape[1]
  num_train = X.shape[0]
  loss = 0.0
  for i in range(num_train):
    scores = X[i].dot(W) # This line
    correct_class_score = scores[y[i]]
    for j in range(num_classes):
      if j == y[i]:
        continue
      margin = scores[j] - correct_class_score + 1 # note delta = 1
      if margin > 0:
        loss += margin

这是在做产品xW,不是应该是Wx吗?我的意思是,
W.dot(X[I])

因为数组的形状分别是
(D,C)
(N,D)
对于
W
X
,你不能直接取点积,而不首先将它们都转置(对于矩阵乘法,它们必须是
(C,D)·(D,N)


由于
X.T.dot(W.T)=W.dot(X)
,实现简单地颠倒了点积的顺序,而不是对每个数组进行变换。实际上,这取决于输入的排列方式。在这种情况下(有些随意)我们决定以更直观的方式安排样本和特征,而不是将dot产品作为
x·W

很好的解释,尽管我认为应该是
xᵀ.点(Wᵀ) == [W.dot(X)]ᵀ
scores = X[i].dot(W)