# Help sketching equation into 3d graph

2 views (last 30 days)
Muhd Farhad on 1 Jun 2021
Answered: Star Strider on 1 Jun 2021 What I got so far for the equation
Z=5-sqrt(1-x.^(2)-(y-abs(x)).^2).*cos(30.*(1-x.^(2)-(y-abs(x)).^(2)))
Then I tried these lines
x=linspace(-1,1, 200);
y=linspace(-1, 1.5, 200);
[X,Y]=meshgrid(x,y);
Z=5-sqrt(1-x.^(2)-(y-abs(x)).^2).*cos(30.*(1-x.^(2)-(y-abs(x)).^(2)))
zlim([1,6]);
surf(X,Y,Z);
It gave me "Z must be a matrix, not a scalar or vector." error.

Star Strider on 1 Jun 2021
The error it throws when I run it here is:
X, Y, Z, and C cannot be complex
This is likely because of the negative values in ‘x’ and ‘y’, however I did not do an in-depth analysis.
Dealing with that produces —
x=linspace(-1,1, 200);
y=linspace(-1, 1.5, 200);
[X,Y]=meshgrid(x,y);
Z=@(x,y) 5-sqrt(1-x.^(2)-(y-abs(x)).^(2).*cos(30*(1-x.^(2)-(y-abs(x)).^(2))));
figure
surf(X,Y,real(Z(X,Y)))
grid on
zlim([1,6])
title('Real Z') figure
surf(X,Y,imag(Z(X,Y)))
grid on
% zlim([1,6])
title('Imag Z') figure
surf(X,Y,abs(Z(X,Y)))
grid on
zlim([1,6])
title('|Z|') figure
surf(X,Y,Z(X,Y))
Error using surf (line 71)
X, Y, Z, and C cannot be complex.
grid on
zlim([1,6])
title('Complex Z')
.

Joseph Cheng on 1 Jun 2021
what you'll need to do is use the function meshgrid() which will then create a 2D matrix for both x and y such that you can get the pair combination of x and y of your linspace
[x y]=meshgrid(x,y);
##### 2 CommentsShowHide 1 older comment
Muhd Farhad on 1 Jun 2021
Owh sry actually I did insert the meshgrid. Updated my post. But still the error shows up.

Girijashankar Sahoo on 1 Jun 2021
% Size of of your output Z must be 200x200 matix
% Try this code for 3D output
x=linspace(-1,1, 200);
y=linspace(-1, 1.5, 200);
for i=1:length(y)
for k=1:length(x)
Z=5-sqrt(1-x.^(2)-(y-abs(x)).^(2).*cos(30*(1-x.^(2)-(y-abs(x)).^(2))));
end
end
zlim([1,6]);
T=rand(200)
surf(x,y,T);

R2021a

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