Matlab中括号在函数输出参数捕获中的用法疑问

Hey there! Let's clear up your confusion around MATLAB's bracket syntax for handling function outputs—this is a super common question when you're learning to work with functions that return multiple values.

1. What does [~,data]=prices_init; mean? #

The ~ in MATLAB is a placeholder for output arguments you don't want to store. Here's the breakdown:

• The function prices_init is designed to return two separate output values.
• The first output is something you don't need, so you use ~ to tell MATLAB to ignore it instead of assigning it to a named variable.
• The second output is assigned to the variable data, which you can then use later in your code.

Think of it like saying: "Run prices_init, throw away the first result, and save the second one as data."

2. How to capture output arguments from functions like union(A,B) #

Let's use the union example from the MATLAB docs: [C,iA,iB] = union(A,B). This function returns three outputs, in order:

• C: The sorted union of elements from A and B
• iA: Indices showing where each element of C appears first in A (0 if the element isn't in A)
• iB: Indices showing where each element of C appears first in B (0 if the element isn't in B)

Here's how you can capture these outputs in practice:

Case 1: Capture all three outputs #

If you need every result, assign each to a named variable in the same order as the function's output:

A = [1, 3, 5];
B = [2, 3, 4];
[my_union, indices_in_A, indices_in_B] = union(A, B);

After running this:

• my_union will be [1, 2, 3, 4, 5]
• indices_in_A will be [1, 0, 2, 0, 3]
• indices_in_B will be [0, 1, 2, 3, 0]

Case 2: Capture only specific outputs #

If you don't need all outputs, use ~ to skip the ones you don't want:

• To get only the union (C) and indices in A (iA):

  [my_union, indices_in_A, ~] = union(A, B);
  

• To get only the indices in B (iB):

  [~, ~, indices_in_B] = union(A, B);
  

• If you only need the first output (C), you can even skip the brackets entirely:

  my_union = union(A, B);
  

Key Rules to Remember #

• Use square brackets [] to capture multiple output arguments.
• Variable names inside the brackets must match the order of the function's declared outputs.
• Use ~ as a placeholder to ignore any output you don't want to store.
• You can omit trailing outputs without using ~ (e.g., [C,iA] = union(A,B) works if you don't need iB).

内容的提问来源于stack exchange，提问作者swedishfished