The operation or expression '(' has no effect

Question

Sarbajit Basu 2021-4-1

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/789824-the-operation-or-expression-has-no-effect

回答： Walter Roberson 2021-4-1

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

Hello all,

I wrote this code to generate multiple sheets having different 5*5 matrices. Somehow, my array ends up empty.

BingoShtGen generates a 5*5 array.

clc
clear all;
numSheets=20;
BngoSt=zeros(6,5,20);
for i=1:numSheets
    BngoSt(1,1,i)=701;
    BngoSt(1,2,i)=702;
    BngoSt(1,3,i)=703;
    BngoSt(1,4,i)=704;
    BngoSt(1,5,i)=705;
end
for i=1:numSheets
    BingoShtGen
    bSt;
    for iC=2:6
        for jC=1:5
            BngoSt(iC,jC,i)=bSt(iC-1,jC);
            bSt(iC-1,jC);
            BngoSt(iC,jC,i);
        end
    end
    BngoSt(:,:,i);
    tt=isempty(BngoSt);
    bSt
    tt
  44;  
end
tt=isempty(BngoSt);
tt;

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Rik 2021-4-1

If you have trouble with Matlab basics you may consider doing the Onramp tutorial (which is provided for free by Mathworks).

Unless BingoShtGen is a script, you aren't actually doing anything with the output. Also, unless bSt is a function, the second line in the inner loop doesn't do anything.

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Answer 1

Walter Roberson 2021-4-1

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/789824-the-operation-or-expression-has-no-effect#answer_664304

We cannot tell whether bSt is a function or a variable. If it is a function then you call it once with two parameters and once with no parameters. If it is an anonymous function then you call it once with two parameters but another time just ask to display the formula. If it is a variable then you do not initialize it.

This is important because if you are initializing it inside a script BingoShtGen then current versions of MATLAB may not know that it is being created inside the script. If you are writing into it inside the script, then at some point before you call BingoShtGen you need to assign something to bSt in order for MATLAB to recognize that it is intended to be a variable (that might be changed inside a script.)