# 2D Surface with periodic structure.

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Michael on 16 Aug 2017
Answered: John BG on 17 Aug 2017
Hello
Below is a section of code that I am working on. The basic idea is to create a surface 30mm square that has a surface that varies according to two sinewave functions. However, my code runs into issue in the Z assignment of the loop. Any help would be appreciated. Also if you have a more compact way
LengthX = 30; % X Length of sample in mm
LengthY = 30; % Y Length of sample in mm
X_k =2; % Number of Periods along X
Y_k =1; % Number of Periods along Y
DegX = pi .* X_k; %Degrees in X
DegY = pi .* Y_k; %Degrees in y
StepSize = 0.05; % Evenly Spaced X,Y gridpoints
x=0:StepSize:LengthX; y= 0:StepSize:LengthY;
NumXStep = DegX / length(x);
NumYStep = DegY / length(y);
Z = zeros(length(x), length(y));
for Counter = 0:1:length(x)
for Counter2 = 0:1:length(y)
% Z =(sin(x)+sin(y)),(-2*pi:0.1:2*pi),(-2*pi:0.1:2*pi);
Z[Counter, Counter2] = sin(NumXStep*Counter)+sin(NumYStep*Counter)
end
end
surf(x,y,Z)

John BG on 17 Aug 2017
Hi Michael
1.
LengthX = .03; % X Length of sample in mm
LengthY = .03; % Y Length of sample in mm
X_k =2; % Number of Periods along X
Y_k =1; % Number of Periods along Y
2.
Don't need DegX DegY
% DegX = 2*pi*X_k; % Degrees in X
% DegY = 2*pi*Y_k; % Degrees in y
3.
The frequencies are needed, but you haven't defined them
T1=.01 % 10mm
T2=.02 % 20mm
f1=1/T1
f2=1/T2
4.
Reduce the step to avoid poor resolution
StepSize = 0.0005; % Evenly Spaced X,Y gridpoints
x=[0:StepSize:LengthX];
y= [0:StepSize:LengthY];
% don't need for loop either
[X,Y]=meshgrid(x,y)
Z=sin(2*pi*f1*X)+sin(2*pi*f2*Y)
.
John BG

Walter Roberson on 16 Aug 2017
In MATLAB, [] is never used for indexing, only for list construction.

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