non square matrix interpolation matlab (colorgraph)

I need help to interpolate non-square matrices in my code, because the code I have been working on works only for square matrices.

Thank you

clc; clear; close all;
V = [600.1 645.23 865.17 1425.8 1254.4; 
    1012.1 1055.8 1006.3 1537.1 1212;
    1296.6 1616.6 1351.9 1393.5 1391.9;
    639.5 868.24 890.56 1644.9 1770.8;
    639.5 868.24 890.56 1644.9 1770.8];
ecol = 30;
ncol = 5 ;
efil = 30;
nfil = 5 ;
%% Matriz de valores para la interpolación del paño
x = (0:ecol:(ncol-1)*ecol);
for i = 1:ncol
    X(i,:)= x;
end

y = (0:efil:(nfil-1)*efil)';
for k = 1:nfil
    Y(:,k)= y;
end

x = (0:1:(ncol-1)*ecol);
for i = 1:(nfil-1)*efil + 1
    Xq(i,:)= x;
end

y = (0:1:(nfil-1)*efil)';
for k = 1:(ncol-1)*ecol + 1
    Yq(:,k)= y;
end

M1q = interp2(X,Y,V,Xq,Yq,'cubic');

%% Ploteo del mapa de velocidades
figure('units','normalized','outerposition',[0 0 1 1])
s = contourf(Xq,Yq,M1q,'--','showtext', 'on');
view(2)
colorbar
set(gca,'Ydir','reverse');
axis tight
title("ST1 [m/s]", 'Fontsize', 15, 'Fontname', 'Times New Roman')
xlabel("Horizontal Displacement [cm]",  'Fontsize', 15, 'Fontname', 'Times New Roman')
ylabel("Vertical Displacement [cm]",  'Fontsize', 15, 'Fontname', 'Times New Roman')

[Carlos]

interesting question..

Answer 1

[Voss]

There is an error in how your matrices X and Y are constructed: nfil and ncol are swapped in those two for loops. It's corrected here:

clc; clear; close all;
V = [600.1 645.23 865.17 1425.8 1254.4; 
    1012.1 1055.8 1006.3 1537.1 1212;
    1296.6 1616.6 1351.9 1393.5 1391.9;
    ...639.5 868.24 890.56 1644.9 1770.8;
    639.5 868.24 890.56 1644.9 1770.8];

ecol = 30;
efil = 30;
[nfil,ncol] = size(V); % avoid hard-coding nfil and ncol; get them from size(V) instead

%% Matriz de valores para la interpolación del paño

x = (0:ecol:(ncol-1)*ecol); % x = (0:ncol-1)*ecol; % would be better

for i = 1:nfil % this was ncol
    X(i,:)= x;
end

y = (0:efil:(nfil-1)*efil)'; % y = (0:nfil-1).'*efil; % would be better

for k = 1:ncol % this was nfil
    Y(:,k)= y;
end

disp(X); disp(Y);

     0    30    60    90   120
     0    30    60    90   120
     0    30    60    90   120
     0    30    60    90   120

     0     0     0     0     0
    30    30    30    30    30
    60    60    60    60    60
    90    90    90    90    90

Note that you can use the meshgrid function to construct X and Y the same way.

[X,Y] = meshgrid(x,y);

disp(X); disp(Y);

     0    30    60    90   120
     0    30    60    90   120
     0    30    60    90   120
     0    30    60    90   120

     0     0     0     0     0
    30    30    30    30    30
    60    60    60    60    60
    90    90    90    90    90

x = (0:1:(ncol-1)*ecol);
for i = 1:(nfil-1)*efil + 1 % could use Xq = repmat(x,nfil,1); instead of a loop
    Xq(i,:)= x;
end

y = (0:1:(nfil-1)*efil)';
for k = 1:(ncol-1)*ecol + 1 % could use Yq = repmat(y,1,ncol); instead of a loop
    Yq(:,k)= y;
end

M1q = interp2(X,Y,V,Xq,Yq,'cubic');

%% Ploteo del mapa de velocidades
figure('units','normalized','outerposition',[0 0 1 1])
s = contourf(Xq,Yq,M1q,'--','showtext', 'on');
view(2)
colorbar
set(gca,'Ydir','reverse');
axis tight
title("ST1 [m/s]", 'Fontsize', 15, 'Fontname', 'Times New Roman')
xlabel("Horizontal Displacement [cm]",  'Fontsize', 15, 'Fontname', 'Times New Roman')
ylabel("Vertical Displacement [cm]",  'Fontsize', 15, 'Fontname', 'Times New Roman')

[Stephen23]

Xq and Yq should also be replaced by MESHGRID. All of the loops are superfluous and inefficient.

[Anghelo Centeno Durand]

Dear thank you for your help

you saved me a week of doubts

[Voss]

You're welcome!