"if sum" (how operator "sum" is possible next to "if"...?)

2 次查看（过去 30 天）
Jinho Lee
Jinho Lee 2022-6-18
回答： Jinho Lee 2022-6-18
I'm trying to undedrstand matlab code for Ising model ("https://kr.mathworks.com/matlabcentral/fileexchange/75149-2d-ising-model")
In the program, there is code like:
if sum(ismember([0:100:iter],i))
I understand ismember but I couldn't understand "if sum"
Q1. Next to "if", there should be logic operator but how can "sum" can be placed
Q2. what is the meaning of sum of logic array, it just number ..?
  1 个评论
per isakson
per isakson 2022-6-18
编辑：per isakson 2022-6-18
Read the documation of if, elseif, else carefully and you will find that if some_thing_numerical is allowed. That's because in Matlab if appeared decades before logical.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（3 个）

Image Analyst
Image Analyst 2022-6-18
The sum can either be 0 or some number. ismember gives you a 1 if the item, i, occurs and 0 if not. It can give you a whole vector os 1's and 0's. The sum counts the number of times there is a 1, and so the if block executes if i is found in the vector [0, 100, 200, ......iter] at least once.
Stephen23
Stephen23 2022-6-18
编辑：Stephen23 2022-6-18
"Next to "if", there should be logic operator"
The IF documentation actually states that it must be an expression. It also states that "An expression is true when its result is nonempty and contains only nonzero elements (logical or real numeric). Otherwise, the expression is false."
"but how can "sum" can be placed"
Just as the IF documentation states, if the SUM() returns only non-zero elements then the expression is considered true. Otherwise it will be false.
"what is the meaning of sum of logic array, it just number ..?"
Yes, SUM() just adds up all of the trues (as ones). In this usage, these are equivalent:
IF SUM(logicalarray)
IF ANY(logicalarray)
Jinho Lee
Jinho Lee 2022-6-18
I got it!
Thanks

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by