writing and call a function in a script with for loops

Question

MICHELE 2014-8-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/151679-writing-and-call-a-function-in-a-script-with-for-loops

回答： Michael Haderlein 2014-8-20

Hi,

I have a question about a function I'm writing and that I do not manage to run in my script file. I enclose the code here:

%% Supply Network Calculation.

% Evaluate the temperature propagation inside a pipe

function [T_s,Q_Ls] = Supply_Network_Calculation (k, n, B_Pipe, C_Pipe, F_Pipe, m,Tg,Tf)

% DECLARE MATRIX U NEED

T=zeros(k,n); Q_Ls=zeros(k,n);

            for  i=1:k-1,
                T(1,1)=Tg(1,1);
                T(i+1,1)=Tg(1,1);
                if m(j)==0.
                    T(1,j+1)=T(2,j);
                else T(1,j+1)=Tf(j,1);
                end
                T(i+1,j+1) = (T(i+1,j)+C_Pipe(j)*(T(i,j+1))+(F_Pipe*2*Tg(j,1)))/B_Pipe(j);
                Q_Ls(i,j)=U_p_Pipe*dA_Pipe*(((T(i,j)+T(i+1,j))/2)-Tg(j,1));
                if Q_Ls(i,j)<0
                   Q_Ls(i,j)= 0;
                end
            end
        end
            T_s=T(k,:)';
       end

I got this error: Subscript indices must either be real positive integers or logicals.

Error in Supply_Network_Calculation (line 10) if m(j)==0.

Error in FEM_Prova_PipeA_corrections_Working (line 282) [T_s2, Q_LsA]= Supply_Network_Calculation (k,n,B_A,C_A,F_A,m_2,Tg,Tf);

I have two questions:

1) Should I define the j index in the function script or would it be recognized within the script?

2) Also, is it a problem having most of my input as matrices?

Thanks for your help in advance

Michele

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Answer 1

Michael Haderlein 2014-8-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/151679-writing-and-call-a-function-in-a-script-with-for-loops#answer_149273

It's generally not ideal to name variables "i" and "j" as they are also used for the imaginary unit. That's exactly what is happening in your function: j is not further defined and so it's used as 1i which of course cannot be an index. Coming to your questions:

1) Where else do you want to define j? I guess it's also some index you want to loop. So you need this loop in your function. If the entire function is inside the j-loop, you need to pass the value of j as argument into the function.

2) It's totally no problem to pass arguments as matrices. Only in case you have very large matrices and you are running out of memory, you should think about other concepts. I doubt that this is the case here.