How do I get a symbolic differentiation of cfit/sfit functions?
16 Ansichten (letzte 30 Tage)
Ältere Kommentare anzeigen
Tim Baur
am 12 Dez. 2019
Kommentiert: Tim Baur
am 2 Jan. 2020
Hi everyone,
I am trying to get the symbolic partial derivative of a sfit function. Best case would be having the differentition as an sfit function, too.
Thanks in advance!
EDIT:
Here's an example:
%data
x = [0.5850;0.0734;0.8223;0.7229;0.9259;0.4926];
y = [0.6549;0.8901;0.5385;0.2822;0.9760;0.0364];
z = [0.3262;0.9730;0.3650;0.3091;0.1209;0.9158];
%surface fit
sf = fit([x, y],z,'poly22')
plot(sf)
% Linear model Poly22:
% sf(x,y) = p00 + p10*x + p01*y + p20*x^2 + p11*x*y + p02*y^2
% Coefficients:
% p00 = 5.048
% p10 = -11.04
% p01 = -1.326
% p20 = 5.179
% p11 = 5.682
% p02 = -3.135
Now I could use the differentiate method to get the derivative at specific points but I would like to have the derived function, like this (witthout having to derive it manually):
% sf_x(x,y) = p10 + 2*p20*x + p11*y
3 Kommentare
Akzeptierte Antwort
Walter Roberson
am 16 Dez. 2019
When sf is the fit object,
f = subs(str2sym(formula(sf)),coeffnames(sf),num2cell(coeffvalues(sf).'));
vars = sym(indepnames(sf));
diff(f, vars(1))
5 Kommentare
Walter Roberson
am 20 Dez. 2019
The upper and lower bounds are in the fit options, which I have it add in via 'options', fitoptions(sf)
Weitere Antworten (0)
Siehe auch
Kategorien
Mehr zu Formula Manipulation and Simplification finden Sie in Help Center und File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!