Scripts works as main code but not as a function

Question

Mizo Amreya 2020-7-15

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/565556-scripts-works-as-main-code-but-not-as-a-function

评论： Mizo Amreya 2020-7-15

采纳的回答： Fangjun Jiang

在 MATLAB Online 中打开

Hello All,

I've written a piece of script in my main code and it's working fine.

I'm trying to move it into a function to make my code more efficient, but it stops working and spits out the following error.

Error: Index exceeds the number of array elements (1).
Error in noflow_boundary (line 27)
            lamdaWG(i) = lamdaO(i+Imax);

Here is my script within my main code:

    for i=1:Imax*Jmax
        if i <= Imax
            lamdaWC(i) = 0;
        else
            lamdaWC(i) = lamdaO(i-Imax);
        end
        if mod(i,Imax) == 1
            lamdaWD(i) = 0;
        else
            lamdaWD(i) = lamdaO(i-1);
        end
        if mod(i,Imax) == 0
            lamdaWF(i) = 0;
        else
            lamdaWF(i) = lamdaO(i);
        end
        if i > (Imax*Jmax)-Imax
            lamdaWG(i) = 0;
        else
            lamdaWG(i) = lamdaO(i+Imax);
        end
    end

And here is how I'm using it in function format:

function [lamdaWC,lamdaWD,lamdaWF,lamdaWG] = noflow_boundary(lamdaO,Imax,Jmax)
% No Flow Boundary Conditions
    for i=1:Imax*Jmax
        if i <= Imax
            lamdaWC(i) = 0;
        else
            lamdaWC(i) = lamdaO(i-Imax);
        end
        if mod(i,Imax) == 1
            lamdaWD(i) = 0;
        else
            lamdaWD(i) = lamdaO(i-1);
        end
        if mod(i,Imax) == 0
            lamdaWF(i) = 0;
        else
            lamdaWF(i) = lamdaO(i);
        end
        if i > (Imax*Jmax)-Imax
            lamdaWG(i) = 0;
        else
            lamdaWG(i) = lamdaO(i+Imax);   % this is the line with the error occurs
        end
    end
end

And here's how I'm calling the function in my main code:

[lamdaWC(i),lamdaWD(i),lamdaWF(i),lamdaWG(i)] = noflow_boundary(lamdaO(i),Imax,Jmax);

Anyone has any idea why the error is popping out in the function and not main code? and how I can resolve it?

Thanking you in advance.

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Answer 1

Fangjun Jiang 2020-7-15

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https://ww2.mathworks.cn/matlabcentral/answers/565556-scripts-works-as-main-code-but-not-as-a-function#answer_466205

在 MATLAB Online 中打开

call it this way

[lamdaWC,lamdaWD,lamdaWF,lamdaWG] = noflow_boundary(lamdaO,Imax,Jmax);

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Mizo Amreya 2020-7-15

Thank you, it worked.

What's the logic behind dropping the counter (i)?

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Answer 2

Tanmay Das 2020-7-15

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链接

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https://ww2.mathworks.cn/matlabcentral/answers/565556-scripts-works-as-main-code-but-not-as-a-function#answer_466211

在 MATLAB Online 中打开

Hi,

I have the understanding that you are passing a single element i.e. lamdaO(i) as an argument but in order to execute your function, you may need to pass the whole array i.e. lamdaO. Also the return types are arrays so you may need to assign the return values of your function to arrays instead. The following code may be helpful for your understanding:

% function definition
function [lamdaWC,lamdaWD,lamdaWF,lamdaWG] = noflow_boundary(lamdaO,Imax,Jmax)
% No Flow Boundary Conditions
    for i=1:Imax*Jmax
        if i <= Imax
            lamdaWC(i) = 0;
        else
            lamdaWC(i) = lamdaO(i-Imax);
        end
        if mod(i,Imax) == 1
            lamdaWD(i) = 0;
        else
            lamdaWD(i) = lamdaO(i-1);
        end
        if mod(i,Imax) == 0
            lamdaWF(i) = 0;
        else
            lamdaWF(i) = lamdaO(i);
        end
        if i > (Imax*Jmax)-Imax
            lamdaWG(i) = 0;
        else
            lamdaWG(i) = lamdaO(i+Imax);   % this is the line with the error occurs
        end
    end
end
% function call
[lamdaWC,lamdaWD,lamdaWF,lamdaWG] = noflow_boundary(lamdaO,Imax,Jmax);