title: Dot product of two vectors in tensorflow
body: <p>I was wondering if there is an easy way to calculate the dot product of two vectors (i.e. 1-d tensors) and return a scalar value in tensorflow.</p>
  
  <p>Given two vectors X=(x1,...,xn) and Y=(y1,...,yn), the dot product is
  dot(X,Y) = x1 * y1 + ... + xn * yn </p>
  
  <p>I know that it is possible to achieve this by first broadcasting the vectors X and Y to a 2-d tensor and then using tf.matmul. However, the result is a matrix, and I am after a scalar.</p>
  
  <p>Is there an operator like tf.matmul that is specific to vectors?</p>