How can I do contour plot?

I would like to use this command. I want to to a contour plot of a square figure. X is the vector who represent the x coordinates of the square figure and Y is a vector who represent the y coordinates of the square figure? If a have a square figure what I have to assume for X and Y inputs?

surf(X,Y,Z)

Matlab said that Z must be a matrix and not a vector. What's the matter?

Answer 1

[Mischa Kim]

Francesco, that is correct. Z must be a matrix, see for example (from the documentation)

 [X,Y] = meshgrid(-8:.5:8);    % create 33-by-33 matrices for X and Y
 R = sqrt(X.^2 + Y.^2) + eps;
 Z = sin(R)./R;                % note, Z is also a 33-by-33  
 surf(X,Y,Z)

where meshgrid is used to create matrices for X and Y. Based on the grid you can compute/assign values to Z .

[Francesco]

But If a have only a vector How can I do it? My Z variable is a column vector. How can I do?

[Francesco]

Kim, I have a square figure. Inside this figure there are some points. At each point inside the square it's associated a numeric value. My goal is to create a map of shades where the highest values are of a certain color (red for example) and the lowest values are of a different one. In practice it is what the leterature said "contour plot". So, I have some points inside the square figure and for each points I have the related numeric values. How do I so the contour plot?

[Walter Roberson]

Like I have told you several times before: use griddata() or trisurfinterp() or scatteredinterpolant()

[Francesco]

I don't have trisurfinterp() or scatteredinterpolant() commands on my MATLAB. I have only griddata(). I have to investigate it!