surf function give wrong graph

I am using surf to draw a surface when given 3 matrix, y_test, z_test, m_k.

y_test and z_test is both 1x100. m_k is a 100x100 matrix.

I have attach mat files of y_test, z_test, m_k.

I use this code:

surf(y_test,z_test,m_k)

And it give the graph like in the surf.png i attach.

This graph is wrong though, i try this point :

plot3(0.7990,8.8932,1.7064,'.r','markersize',10);

It is the red point you see in the graph. It is way off, not even close to the surface.

If i use loops to pot this point by point, like the code below:

count_i = 0;
count_j = 0;
for i = y_test
    count_i = count_i + 1;
    if count_j == 100
        count_j = 0;
    end
    for j = z_test
        count_j = count_j + 1;
        m_k(count_i,count_j) =  - m_k_ranhTQ_1(x,input,beta0,kbeta_bao_hoa,x_delta,kI,Ka,time,Z1,Z2,i,j);
        plot3(y_test(count_i),z_test(count_j),m_k(count_i,count_j),'.r','markersize',1);
        hold on;
    end
end

It will give correct graph, like in the correct plot.png i attach. The redder point i use to check is on the "surface" of points.

Can someone explain this? Is the surf function some how alter the results to get a smooth surface or something?

Answer 1

[Voss]

Try this instead:

load('m_k.mat');
load('y_test.mat');
load('z_test.mat');

% surf(y_test,z_test,m_k);
surf(y_test,z_test,m_k.');

hold on
plot3(0.7990,8.8932,1.7064,'.r','markersize',10);

It looks like, the way m_k was calculated the first index (rows) corresponds to y_test and 2nd index (columns) corresponds to z_test, but in surf() it has to be the other way around (this is hard to notice when the matrix is square). Observe:

figure
try
    surf(1:4,1:10,randn(4,10)) % generates an error
catch ME
    disp(ME.message);
end

Data dimensions must agree.

surf(1:4,1:10,randn(10,4)) % works

In surf(), vector X goes along the second dimension of matrix Z, and vector Y goes along the first dimension of Z.

[quan ng]

thanks a lot, it works! And i thought i have to use the point by point graph if i can't figure out how to use the surf function

[Voss]

I'm glad it's working! If you don't have other questions about this, do you mind marking my answer as 'Accepted'? I appreciate it!

[quan ng]

i forgot about it. Accepted!

[Voss]

Thank you!