1D interpolation with non-monotonic scattered data

50 Ansichten (letzte 30 Tage)
Kim
Kim am 20 Okt. 2014
Beantwortet: AlexL am 19 Jul. 2022
I cant figure out how do 1D interpolation with scattered data. I know how to get it working with 2D interpolation, but scatteredinterpolant only works with 2D or more. Thank you for your help!

Melden Sie sich an, um diese Frage zu beantworten.

Akzeptierte Antwort

Andrei Bobrov
Andrei Bobrov am 20 Okt. 2014
Bearbeitet: Andrei Bobrov am 20 Okt. 2014
Use griddedInterpolant-class
small example:
x = rand(30,2); % you data
x1 = sortrows(x,1);
F = griddedInterpolant(x1(:,1),x1(:,2));
out = F(xinput);
  2 Kommentare
Kim
Kim am 20 Okt. 2014
I just tried it and I got the following message: Error using griddedInterpolant The grid vectors are not strictly monotonic increasing.
Andrei Bobrov
Andrei Bobrov am 20 Okt. 2014
please see small example in my answer

Melden Sie sich an, um zu kommentieren.

Weitere Antworten (2)

Riley
Riley am 5 Okt. 2016
Just ran into this same issue, however the solution posted seems to avoid tackling an important detail here- griddedInterpolant, unlike scatteredInterpolant, doesn't remove repeated index points (at least, on 2015a). For example:
x = rand(30,2); % clean data
x1 = sortrows(x,1);
F = griddedInterpolant(x1(:,1),x1(:,2)); % this is fine
x_repeat = x1(:,1);x_repeat(2) = x_repeat(3); % introduce a repeated index point
F = griddedInterpolant(x_repeat,x1(:,2)); %produces an error
compare that to the scatteredInterpolant class-
x = rand(30,3); % clean data
x1 = sortrows(x,1);
x_repeat = x1(:,1:2);x_repeat(2,:) = x_repeat(3,:); % introduce a repeated index point
F = scatteredInterpolant(x_repeat,x1(:,3)); %rather than throwing an error, shows a warning and cleans your data for you
however, as scatteredInterpolant requires at least 2 dimensions for its indices, this doesn't work for 1d interpolation. Clearly at this point you can add your own cleaning method, but if you are using this class chances are you are trying to avoid writing that sort of code in the first place. As such, here's a hack I used to use the scatteredInterpolant cleaning method on a 1d data set-
xi = rand(30,1);%indices
x = sort(xi);
v = rand(30,1);% values
xq = [0.5 0.6];% query indices
x(2) = x(3);% the repeated index
Fs = scatteredInterpolant(x*ones(1,2),v);%make 1d into 2d
%note that the sane thing to do doesn't work: vq = Fs(xq'*ones(1,2)) produces an empty vector
F = griddedInterpolant(Fs.Points(:,1),Fs.Values);
vq = F(xq);
this produces plenty of warnings and will make you feel bad, but if you want a quick solution it will work
AlexL
AlexL am 19 Jul. 2022
I was also curious to solve this issue.
I wrote a short function that was helpful for me. You're welcome to try it (attached).

Kategorien

Mehr zu Variables finden Sie in Help Center und File Exchange

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by