X and Y co-ordinates of a surface?

hi all, i have a surface z=f(x,y).......may i obtain values of x and y if z is known?.....is there any tool for that

Answer 1

[Mike Garrity]

Depending on the details of your surface, it can be simple, but for the general case, you're probably looking for contour . It takes the same arguments as surface, but gives you a curve which is passes through all of the X,Y positions with a specified Z.

For example:

[x,y,z] = peaks;
C = contour(x,y,z,'LevelList',0);

If you don't want to draw the results, you can use contourc instead of contour.

The format of the returned matrix C is explained here . It's a bit complicated, because there might be several loops of locations with the same Z. The example above returns something like this:

If you look at C, you'll see that the first column is:

>> c(:,1)

ans = 

       0
      70

The 0 in the first row is the Z level, and the 70 in the second row says that there are 70 X,Y pairs in this loop. That means that c(:,2) through c(:71) are the coordinates of the first loop.

Then if we skip ahead to c(:72), we find:

>> c(:,72)

ans = 

        0
       68

That means that c(:,73) through c(:,140) are the coordinates of the second loop. Finally, if we look at c(:,141), we find:

>> c(:,141)

ans = 

        0
        9

which means that c(:,142) through c(:,150) contain the coordinates of the last loop, which is that tiny one in the center of the picture.

Does that make sense?