MATLAB: How to use the ppval, pp and spline in this situation

interpolationMATLABppppvalspline

I have the following in a code:
pp=spline(diameter,nbdensity);
all(i,j) = ((diameter(i,1)^3)-(diameter(j,1)^3))^(1/3);       
finp(i,j) = ppval(pp,all(i,j));
I need to find the interpolated value of "nbdensity" at a given value of "all". How would I express it using the above? Would the following be correct?
nbdensity(i)*finp(i,j)

Best Answer

Given data vectors x and y. f = spline(x, y) function returns a piecewise-polynomial which models the best relation (in the least square sense) f:x->y. After estimating the polynomial, if you want to find the value of y at some arbitrary value of x, you can just evaluate piecewise polynomial f at. In MATLAB you can use ppval function to evaluate the piecewise polynomial f.
Related Question