matlab - 笛卡尔积的Matlab矢量化

Question

假设我有两个数组 X 和 Y，我需要一个矩阵 M(i, j) = some_func(X(i), Y(j))。我怎样才能在不使用循环的情况下得到它？

Answer 1

最好的答案是使用 bsxfun，如果它是一个选项。根据 bsxfun 的帮助，它适用于任何一般的二元函数，只要：

  FUNC can also be a handle to any binary element-wise function not listed
    above. A binary element-wise function in the form of C = FUNC(A,B)
    accepts arrays A and B of arbitrary but equal size and returns output
    of the same size. Each element in the output array C is the result
    of an operation on the corresponding elements of A and B only. FUNC must
    also support scalar expansion, such that if A or B is a scalar, C is the
    result of applying the scalar to every element in the other input array.

如果您的函数只接受标量输入，那么循环是简单的替代方案。

Answer 2

很难回答您的模糊问题，这最终取决于您的功能。您可以做的是使用meshgrid然后执行您的操作，通常使用点运算符

例如

x = 1:5;
y = 1:3;

[X,Y] = meshgrid (x,y)

M = X.^Y;