Vectors to Contour3...confused

I have 3 linked vectors from physical data: call them vectors a,b,c. A given cell entry across a,b,c are linked (taken at the same time).

I'd like to plot this data as a 3D contour:

x1=a(1), y1=b(1), z1=c(1) is a coordinate point to plot

x2=b(2),... are another coordinate point, etc.

How can I make the right Z matrix? Matlab examples frustratingly always have computable functions which don't help.

I've read 15-20 posts on this but have clear answer.

[Vaidyanathan Thiagarajan]

Hello Paul,

I believe this is what you are looking for :

%1D vector that defines the x,y, and z coordinates
x = [0.2 0.4 0.6 1.0 0.2 0.4 0.6 1.0 0.2 0.4 0.6 1.0 0.2 0.4 0.6 1.0];
y = [0.25 0.25 0.25 0.25 0.5 0.5 0.5 0.5 0.75 0.75 0.75 0.75 1.0 1.0 1.0 1.0];
z = x.^2 + y.^2;
%Now, reshape all of them into a 2D matrix as required by the contour3 function 
XMat = reshape(x,4,4);
YMat = reshape(y,4,4);
ZMat = reshape(z,4,4);
%Plot the contour
contour3(XMat,YMat,ZMat,30);

As the documentation indicates, the following are the conditions on X,Y, and Z :

a. If X and Y are vectors, then length(X) must equal size(Z,2) and length(Y) must equal size(Z,1). The vectors must be strictly increasing or strictly decreasing and cannot contain any repeated values.

b. If X and Y are matrices, then their sizes must equal the size of Z. Typically, you should set X and Y so that the columns are strictly increasing or strictly decreasing and the rows are uniform (or the rows are strictly increasing or strictly decreasing and the columns are uniform).

This means that if your 1D x,y, and z vectors don't obey this condition, then you might not get the desired result. Hence, it is first necessary to induce an order to the 1D vectors and then reshape them to 2D matrices appropriately before passing it on to the contour3 function.

In the above code snippet, I have directly converted the 1D arrays into equivalent 2D matrices using the 'reshape' function as my data is already ordered. However, in your case, you might have to induce an order first before reshaping.

For more details on reshape function, please refer to the following link :

https://www.mathworks.com/help/matlab/ref/reshape.html

Hope this helps.

Vaidyanathan