Generate a logarithmic regression of xlsdata and plot it

Question

Sergio 2024-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/2085388-generate-a-logarithmic-regression-of-xlsdata-and-plot-it

评论： Sergio 2024-2-26

data.xlsx

I have the given data in the xls file. I tried to convert the Var1 and Var2 to log10 values, and then do a regression with the given command. But I get an error.

Incorrect number or types of inputs or outputs for function log10.

Error in uppgift44 (line 2)

X=log10('Var1'); Y=log10('Var2'); % convert both variables to log's

P=readtable('data')
X=log10('Var1'); Y=log10('Var2');  % convert both variables to log's
b=polyfit(X,Y,1);        % estimate coefficients
yhat=10.^[polyval(b,[X(1) X(end)])];  % evaluate at end points
loglog(x,y)
hold on
loglog([x(1) x(end)],yhat) % add fitted line
plot(ans)

Where is the error here?

Thanks!

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Answer 1

Dyuman Joshi 2024-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/2085388-generate-a-logarithmic-regression-of-xlsdata-and-plot-it#answer_1414448

在 MATLAB Online 中打开

That is not how you access data inside Tables. Go through this for more information - Access Data in Tables

%% Provide the filename with extension
P=readtable('data1.xlsx');
%% Use dot indexing to access the data
X=log10(P.Var1);
Y=log10(P.Var2);  % convert both variables to log's
b=polyfit(X,Y,1);        % estimate coefficients
yhat=10.^[polyval(b,[X(1) X(end)])];  % evaluate at end points
%% Variable names are capital
figure
loglog(X,Y,'r')
hold on
plot([X(1) X(end)],yhat,'b') % add fitted line

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John D'Errico 2024-2-22

编辑：John D'Errico 2024-2-22

Correct of course. But honestly, the subtle error you corrected in your answer is symptomatic of the reason I have begun to strongly dislike tables in MATLAB.

Tables allow users to use MATLAB as if they are still using a spreadsheet.

Why learn MATLAB itself as a language, when you have a spreadsheet inside MATLAB right there? As it is things are bad enough that we have stuents who insist on doing everything from a spreadsheet and directly back into a spreadsheet. That is, I have this data in a spreadsheet, will someone please show me how to do computation X on the spreadsheet, and then return the results as a spreadsheet.

And, yes, I can sort of understand the reason why tables were introduced into MATLAB. It was an interesting idea, as it allows you to nicely collect your data for display, to view your data. As it is, I often group my data into a 2-d array, a nice way to compare two columns perhaps side by side. A table is even nicer for display purposes. The problem arises in my eyes when it becomes too easy, too tempting to do all of your computations there too.

Sorry, just a rant, that probably belongs in a discussion.