---

19.7示例¶

以下是Octave实验者提出的向量化问题及其解决方案的示例。

• 对于向量A,以下循环

  n = length (A) - 1;
  B = zeros (n, 2);
  for i = 1:n
    ## this will be two columns, the first is the difference and
    ## the second the mean of the two elements used for the diff.
    B(i,:) = [A(i+1)-A(i), (A(i+1) + A(i))/2];
  endfor
  

  可以变成以下一个衬垫:

  B = [diff(A)(:), 0.5*(A(1:end-1)+A(2:end))(:)]
  

  请注意使用冒号索引将中间结果展平为列向量。这是一个常见的向量化技巧。