I need to get the r-square of the model

Hi, I need to get the r-square of the model I made. It contains 3 variables (x,y,z). I don't know how to use matlab so I turn to the community, because I don't understand the answers from other forums. PLEASE HELP ME :(

(I use Matlab R2019a)

clear;
pga_x = load('PGA.txt'); %Text file with 115 data
clt_y= load('CLT.txt'); %Text file with 3 data
costo_z=load('COSTOFEMA.txt'); %Text file with 115 data
%c1_z= costo_z(:,1);
%c2_z= costo_z(:,2);
%c3_z= costo_z(:,3);
%c4_z= costo_z(:,4);

[xdata, ydata, zdata] = prepareSurfaceData(pga_x, clt_y, costo_z);

sf = fit([xdata, ydata], zdata, 'poly11');
disp(sf);
a = plot(sf,[xdata, ydata], zdata);
hold on
legend( a, 'Ajuste de curva Lineal', '%CLT vs. PGA(g), Costo US($)', 'Location', 'NorthEast' );
xlabel('PGA (g)');
ylabel('%CLT');
zlabel('Costo de reparación US $');
colormap(cool);

Answer 1

[the cyclist]

Instead of calling the fit function with one output

sf = fit([xdata, ydata], zdata, 'poly11');

call it with two outputs

[sf, gof] = fit([xdata, ydata], zdata, 'poly11'); % Get goodness-of-fit output

and then

gof.rsquare

should give you the R^2 value. This is described in the Output Arguments section of the documentation of the fit function.