Problems using polyfit in a for loop

Question

Bob 2014-12-14

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https://ww2.mathworks.cn/matlabcentral/answers/166561-problems-using-polyfit-in-a-for-loop

回答： Star Strider 2014-12-14

I am getting an error when I try to run this polyfit. I think the problem is the values I am putting for xfit1 in the polyfit formula. What values should I put for xfit1 to fix my code?

Error Message: Error using polyfit (line 50) X and Y vectors must be the same size.

My Code:

Z=[3 1];  
for i=1:length(Z);  
    A(i)=Z(i)+2;  
    B(i)=Z(i)-7;  
    xfit=[0 1];  
    yfit1(:,i)=[A(i),B(i)]  
    pfit1(:,i)=polyfit(xfit1,yfit1(:,i),1);  
end

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Answer 1

Star Strider 2014-12-14

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You had the indexing reversed in ‘yfit1’ and ‘pfit1’. This works:

Z=[3 1];  
for i=1:length(Z);  
    A(i)=Z(i)+2;  
    B(i)=Z(i)-7;  
    xfit1=[0 1];  
    yfit1(i,:)=[A(i),B(i)];
    pfit1(i,:)=polyfit(xfit1,yfit1(i,:),1);  
end