Plotting a 3-D Function with Interpolated Shading

I am having issues with the meshgrid ( http://www.mathworks.com/help/matlab/ref/meshgrid.html ) function. I need X and Y to be a 21x25 matrix but this function is only generating a 21x26 matrix when I use the following command:

    [X,Y] = meshgrid(0:.04:1, 0:.024:0.5);                               
    Z = cos(2*pi*(3.*X - 4.*Y))                                        
    surf(X,Y,Z)

X and Y are bounded by the following:

0<= X <= 1 (Need 25 data points)

&

0<= Y <= 0.5 (Need 21 data points)

I figure that 1 / 25 should give me 25 total data points for the X bounary and 0.5 / 21 should give me 21 total data points for the Y boundary.

However, meshgrid is giving me a 21x26 matrix. Is the parameter argument incorrect for the function?

Answer 1

[Evan]

    [X,Y] = meshgrid(linspace(0,1,25), 0:.024:0.5);                               
    Z = cos(2*pi*(3.*X - 4.*Y))                                        
    surf(X,Y,Z)

The linspace command will gave you the same result as 0:1/24:1, as I believe increments of 1/24 would give you the number of data points you desire.

It's a bit easier to use linspace instead of the colon operator when your main concern is the length of the array you're creating, not the spacing.

[Jonathan]

That did it for me! Although, why wouldn't manually incrementing by 0.04 work? For instance I used the command:

[X,Y] = meshgrid(0:.04:1, 0:.024:0.5);

This should be the same as saying,

[X,Y] = meshgrid(0:1/24:1, 0:.024:0.5);

or

[X,Y] = meshgrid(linspace(0,1,25), 0:.024:0.5);

Either of the three should work the same, correct?

[Evan]

In decimal form, 1/24 is 0.0416666667. While it does round to 0.04, 0.04 is equal to 1/25 which will give you 26 elements.

[Jonathan]

Sounds great. That was my mistake. I was assuming the correct expression would be 1/25 because I need 25 data points so (1-0)/25, but I was neglecting that were are starting at 0 and therefore I didn't account for it.

Thanks for your help Evan. I greatly appreciate it!

[Evan]

I make that same mistake quite often. And no problem! Glad you have it working.