How to write integral equation ?

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Michael Crown 2020-9-5

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https://ww2.mathworks.cn/matlabcentral/answers/589522-how-to-write-integral-equation

回答： Michael Crown 2020-9-10

采纳的回答： David Hill

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I like to check if my code represent the equation. Please help

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David Hill 2020-9-5

Yes, attach full code and ask a specific question.

Michael Crown 2020-9-5

attached @David Hill

All i need is to calculate DaveA and DaveB using the attached equation. I am not sure what i have i right.

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David Hill 2020-9-5

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https://ww2.mathworks.cn/matlabcentral/answers/589522-how-to-write-integral-equation#answer_490453

在 MATLAB Online 中打开

Not sure if your Ca is sorted. Yes, you have a stream of data that is being integrated. The proper function is trapz(). Providing your full code helped significantly. I assume you want your data sorted before integrating.

[Ca,idx]=sort(dataB(:,1));
Da=dataB(:,2);
Da=Da(idx);%aligns Da to sorted Ca
DaveA=trapz(Ca,Da)/(Ca(end)-Ca(1));

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Michael Crown 2020-9-6

Is there another way in such that DaveM is calculated from the value I got for D vz c? This code you shared messed the plots.

Michael Crown 2020-9-6

Hello, if you don’t mind, help modify code such that DaveM will be calculated from the already obtained D vrs c from my data without sorting . The one you sent to me isn’t working.

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Michael Crown 2020-9-5

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https://ww2.mathworks.cn/matlabcentral/answers/589522-how-to-write-integral-equation#answer_490459

Forgive me for too many requests. Please can you put the modification in the code and send back. I am not clear

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Michael Crown 2020-9-5

Hello David, I am not able to calcualte DaveM. can you help check?

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Michael Crown 2020-9-6

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编辑：Walter Roberson 2020-9-6

在 MATLAB Online 中打开

Now, i am totally confused, it didnt run

time = 223*60*60;	% diffusion time in seconds	
data = load ('File 223.txt'); % read in data
dataB = load ('File 2233.txt');
[pos,idx]=sort(data(:,1)); 
c=data(:,2 ); 
D= D(idx ); 
c=smooth(c,.2 ); 
D = smooth(D, .2);
cMax=c(end ); 
cMin=c(1 ); 
pos=smooth(c,.2 ); 
matanoPos= pos(matanoIndex ); 
posn =(pos - matanoPos ); 
slope = 1/2*diff(posn(1:end-1))./diff(c(1:end-1))+diff(posn(2:end))./diff(c(2:end )); 
i= cumsum(1/2*movsum(posn(2:end),2,'Endpoints','discard').*diff(c(1:end-1 ))); 
c=c(2:end-1 ); 
D=-1/(2*time).*slope.*i ; 
DaveM=trapz(c,d)/(cMax-cMin);
[cA,idx] = sort(dataB(:,1));
DA=DA(idx);
DaveA = trapz(cA,DA)/(cAMax-cAMin); %cAMax = cA(end), cAMin = cA(1)
semilogy (c,D,'r*') %create a plot using a base 10 logarithmic scale for y-axis and a linear scale for x-axis
hold on
semilogy(cA,DA, 'k*')
title('D of the Cu–Zn binary system at 700degC, 501hrs')
xlabel('Concentration, Zn(at.%)')
ylabel('Interdiffusion Coefficient (m2/s)')
legend('Mike','','Author')