MATLAB Answers

0

interpolation of scatter data

Asked by Solmaz Kahourzade on 4 May 2018
Latest activity Commented on by Star Strider
on 4 May 2018
Hi, I am new in Matlab and I have difficulty in solving this problem. I have a matrix as bellow where Fd is a function of Id and Iq and also Fq is a function of Id and Iq. I want to extend my results for a 128*128 matrix of Id and Iq. The code that I used is as:
Id_vector = linspace(-200,0,128);
Iq_vector = linspace(-200,0,128);
[ Id , Iq ] = meshgrid(Id_vector,Iq_vector);
but I can not create a function for Fd and Fq using two variables. I tried the interp1 and ppval without any success. would you please help me?
Id Iq Fd Fq
0 0 0.001 -0.172
-50.0 0 0.001 -0.186
-100 0 0.001 -0.196
-150 0 0.001 -0.204
-200 0 0.001 -0.210
0 -50 -0.020 -0.172
-50 -50 -0.019 -0.186
-100 -50 -0.017 -0.196
-150 -50 -0.016 -0.204
-200 -50 -0.015 -0.210
0.0 -100.0 -0.042 -0.171
-50.0 -100.0 -0.039 -0.185
-100.0 -100.0 -0.036 -0.195
-150.0 -100.0 -0.034 -0.203
-200.0 -100.0 -0.032 -0.209
0.0 -150.0 -0.064 -0.168
-50.0 -150.0 -0.060 -0.182
-100.0 -150.0 -0.056 -0.192
-150.0 -150.0 -0.052 -0.200
-200.0 -150.0 -0.049 -0.206
0.0 -200.0 -0.085 -0.164
-50.0 -200.0 -0.079 -0.178
-100.0 -200.0 -0.074 -0.188
-150.0 -200.0 -0.069 -0.196
-200.0 -200.0 -0.065 -0.203

  0 Comments

Sign in to comment.

2 Answers

Answer by Star Strider
on 4 May 2018
 Accepted Answer

Your data are gridded, so you simply need to reshape the vectors to create matrices:
% Id Iq Fd Fq
M = [ 0 0 0.001 -0.172
-50.0 0 0.001 -0.186
-100 0 0.001 -0.196
-150 0 0.001 -0.204
-200 0 0.001 -0.210
0 -50 -0.020 -0.172
-50 -50 -0.019 -0.186
-100 -50 -0.017 -0.196
-150 -50 -0.016 -0.204
-200 -50 -0.015 -0.210
0.0 -100.0 -0.042 -0.171
-50.0 -100.0 -0.039 -0.185
-100.0 -100.0 -0.036 -0.195
-150.0 -100.0 -0.034 -0.203
-200.0 -100.0 -0.032 -0.209
0.0 -150.0 -0.064 -0.168
-50.0 -150.0 -0.060 -0.182
-100.0 -150.0 -0.056 -0.192
-150.0 -150.0 -0.052 -0.200
-200.0 -150.0 -0.049 -0.206
0.0 -200.0 -0.085 -0.164
-50.0 -200.0 -0.079 -0.178
-100.0 -200.0 -0.074 -0.188
-150.0 -200.0 -0.069 -0.196
-200.0 -200.0 -0.065 -0.203];
IdMtx = reshape(M(:,1), 5, []);
IqMtx = reshape(M(:,2), 5, []);
FdMtx = reshape(M(:,3), 5, []);
FqMtx = reshape(M(:,4), 5, []);
figure(1)
surf(IdMtx, IqMtx, FdMtx)
grid on
xlabel('Id')
ylabel('Iq')
zlabel('Fd')
figure(2)
surf(IdMtx, IqMtx, FqMtx)
grid on
xlabel('Id')
ylabel('Iq')
zlabel('Fq')
Use the griddata (link) function to interpolate to a finer mesh. I would not extrapolate beyond the limits of your data, because you have no idea what your data are outside those limits.
IdIq = linspace(min(IdMtx(:)), max(IdMtx(:)), 250); % Create Interpolation Vector (250 elements)
[Idi,Iqi] = meshgrid(IdIq); % Create Interpolation Matrices
Fdi = griddata(IdMtx, IqMtx, FdMtx, Idi, Iqi); % Interpolate ‘Fd’
Fqi = griddata(IdMtx, IqMtx, FqMtx, Idi, Iqi); % Interpolate ‘Fq’
figure(3)
mesh(Idi, Iqi, Fdi)
grid on
xlabel('Id')
ylabel('Iq')
zlabel('Fd')
figure(4)
mesh(Idi, Iqi, Fqi)
grid on
xlabel('Id')
ylabel('Iq')
zlabel('Fq')
I use the default 'linear' interpolation method here, because it seems appropriate to these surfaces.
Experiment to get the result you want.

  2 Comments

Dear Star Strider,
Thank you so much. It is exactly what I needed.
My pleasure.
If my Answer helped you solve your problem, please Accept it!

Sign in to comment.


Answer by KSSV
on 4 May 2018

A = [0 0 0.001 -0.172
-50.0 0 0.001 -0.186
-100 0 0.001 -0.196
-150 0 0.001 -0.204
-200 0 0.001 -0.210
0 -50 -0.020 -0.172
-50 -50 -0.019 -0.186
-100 -50 -0.017 -0.196
-150 -50 -0.016 -0.204
-200 -50 -0.015 -0.210
0.0 -100.0 -0.042 -0.171
-50.0 -100.0 -0.039 -0.185
-100.0 -100.0 -0.036 -0.195
-150.0 -100.0 -0.034 -0.203
-200.0 -100.0 -0.032 -0.209
0.0 -150.0 -0.064 -0.168
-50.0 -150.0 -0.060 -0.182
-100.0 -150.0 -0.056 -0.192
-150.0 -150.0 -0.052 -0.200
-200.0 -150.0 -0.049 -0.206
0.0 -200.0 -0.085 -0.164
-50.0 -200.0 -0.079 -0.178
-100.0 -200.0 -0.074 -0.188
-150.0 -200.0 -0.069 -0.196
-200.0 -200.0 -0.065 -0.203] ;
Id = A(:,1) ; Iq = A(:,2) ; Fd = A(:,3) ;Fq = A(:,4) ;
% Do interpolation
Id_vector = linspace(-200,0,128);
Iq_vector = linspace(-200,0,128);
[ Idi , Iqi ] = meshgrid(Id_vector,Iq_vector);
F1 = scatteredInterpolant(Id,Iq,Fd) ;
Fdi = F1(Idi,Iqi) ;
F2 = scatteredInterpolant(Id,Iq,Fq) ;
Fqi = F2(Idi,Iqi) ;

  0 Comments

Sign in to comment.