Save error R² of an interpolation curve in variable

A polynomial compensation curve with its coefficients is determined at various measuring points.

 myfit=fit(x,y,'poly2');
 A=myfit.p1
  B=myfit.p2
   C_=myfit.p3

Now i still need the error of this interpolation (R²). Can it also be read and stored in a variable?

Answer 1

[John D'Errico]

You misunderstand the idea of interpolation, confusing it with approximation.

R^2 is identically 1 for an interpolation, since interpolation is defined so that it always predicts the original data. So an interpolating spline has always zero residuals in theory, therefore, R^2 == 1.

Anyway, just read the help for fit!!!!!!!

x = rand(10,1);
y = randn(size(x));
[mdl,G] = fit(x,y,'poly2')

y = randn(size(x));
[mdl,G] = fit(x,y,'poly2')
mdl = 
     Linear model Poly2:
     mdl(x) = p1*x^2 + p2*x + p3
     Coefficients (with 95% confidence bounds):
       p1 =       1.399  (-3.992, 6.791)
       p2 =     -0.1758  (-5.699, 5.347)
       p3 =     -0.4521  (-1.34, 0.4359)
G = 
  struct with fields:

           sse: 2.72060725180258
       rsquare: 0.468192584870819
           dfe: 7
    adjrsquare: 0.316247609119625
          rmse: 0.623424557447764

As you can see, G has fields that answer your question: G.rsquare, and G.adjrsquare.