MATLAB: How to enter the R-square fit formula in the m-file

r-square fit

I need to calculate the R-square fit for the model output. I have the formula for calculating it, but how to give it in the code and what is the plot command to get the r-square fit?

Please do help me.

Best Answer

Residual sum of squares

residsumsq = norm(y-yhat,2)^2;

Total sum of squares

tsumsq = norm(y-mean(y),2)^2;
R2 = 1-(tsumsq/residsumsq);

Related Solutions

MATLAB: Least squares regression of a quadratic without bx term.

Try this:

DM = [x(:).^2 ones(size(x(:)))];                        % Design Matrix
B = DM \ y(:);                                          % Parameters
yfit = DM * B;                                          % Calculated Fit
SStot = sum((y-mean(y)).^2);                            % Total Sum-Of-Squares
SSres = sum((y(:)-yfit(:)).^2);                         % Residual Sum-Of-Squares
Rsq = 1-SSres/SStot;                                    % R^2

To plot it:

figure
plot(x, y, 'p')
hold on
plot(x, yfit, '-r')
hold off
grid

MATLAB: M-file function

Your function is calling itself without approaching any convergance or something that will allow it to end. Therefore it will run forever and eventually out of memory (hence the error). Try splitting it up into a script and a function as so:

Script:

 %creating window of plot from -5 to 50 using stepsize 0.25 for t x-axis
 %t should be on the x axis, v should be on the y axis
 k=0; 
for i= -5:.25:50
    k = k+1;
    t(k)=i;
    v(k)=vPieceWise(t(k));
end 
plot(t,v);
 
figure
plot(t,v);
hold on

Function:

%Part A: Mfile function to compute v as a function of t
function v = vPieceWise(t)
 if (t < 0)
        v = 0;
    elseif (0 <= t)&&(8<=16)
        v = -5*t+10*t.^2;
    elseif (8<=16)&&(t<=16)
        v = 624 - 3*t;
    elseif (t<=16)&&(t<=26)
        v = 12*(t-16).^2+36*t;
    elseif (26<t)
        v = 2136*exp(-0.1*(t-26));
 end

Best Answer

Related Solutions

MATLAB: Least squares regression of a quadratic without bx term.

MATLAB: M-file function

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