Error using surf X, Y, Z, and C cannot be complex error

i run this code, but get this message Error using surf X, Y, Z, and C cannot be complex error, any idea what is wrong?

clc

theta5=[0:0.2:pi];

theta4=[0:0.2:pi];

for M=1:length(theta4)

for N=1:length(theta5)

H(M,N)=cos(theta4(M))*sin(theta5(N));

end

end

[X,Y]=meshgrid(theta4,theta5);

surf(Y,X,H)

Answer 1

[John BG]

Hi

this is John BG <mailto:[e-mail] [e-mail]>

The problem is not in solving

x = 0:0.8:pi;
A = sin(x).^(1/3)
B = cos(x).^(1/3)

the operator

.^

solves for either real or complex.

The problem lays in the fact that surf doesn't take in complex values.

To solve the long expression of H, since you are dealing with complex numbers, you have to plot 2 surfs, not one: Real and Imaginary, or Modulus and Phase

clc
theta5=[0:0.1:pi];
theta4=[0:0.1:pi];
[X,Y]=meshgrid(theta4,theta5);
H=(((((cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).*(cos(X).^2.*cos(Y).^2-cos(X).^2*sin(X).^2+cos(Y).^2.*sin(X).^2+cos(X).^2.*cos(Y).^4.*sin(X).^2+2*cos(X).^2.*sin(X).^2.*sin(Y).^2-cos(Y).^2.*sin(X).^2.*sin(Y).^2-cos(X).^2.*sin(X).^2.*sin(Y).^4))./6+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^3./27+(cos(X).^2.*cos(Y).^2.*sin(X).^2)./2-(cos(X).^2.*cos(Y).^6.*sin(X).^2)./2-(cos(X).^2.*cos(Y).^2.*sin(X).^2.*sin(Y).^2)./2-cos(X).^2.*cos(Y).^4.*sin(X).^2.*sin(Y).^2).^2-((cos(X).^2.*cos(Y).^2)./3-(cos(X).^2.*sin(X).^2)./3+(cos(Y).^2.*sin(X).^2)./3+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(X).^2+sin(X).^2.*sin(Y).^2).^2./9+(cos(X).^2*cos(Y).^4.*sin(X).^2)./3+(2.*cos(X).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(Y).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(X).^2.*sin(X).^2.*sin(Y).^4)./3).^3).^(1/2)-((cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).*(cos(X).^2.*cos(Y).^2-cos(X).^2.*sin(X).^2+cos(Y).^2.*sin(X).^2+cos(X).^2.*cos(Y).^4.*sin(X).^2+2.*cos(X).^2.*sin(X).^2.*sin(Y).^2-cos(Y).^2.*sin(X).^2.*sin(Y).^2-cos(X).^2.*sin(X).^2.*sin(Y).^4))./6-(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^3./27-(cos(X).^2.*cos(Y).^2.*sin(X).^2)./2+(cos(X).^2.*cos(Y).^6.*sin(X).^2)./2+(cos(X).^2.*cos(Y).^2.*sin(X).^2.*sin(Y).^2)./2+cos(X).^2.*cos(Y).^4.*sin(X).^2.*sin(Y).^2).^(1/3)+cos(X).^2./3-cos(Y).^2./3+sin(X).^2./3+((cos(X).^2.*cos(Y).^2)./3-(cos(X).^2.*sin(X).^2)./3+(cos(Y).^2.*sin(X).^2)./3+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^2./9+(cos(X).^2.*cos(Y).^4.*sin(X).^2)./3+(2*cos(X).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(Y).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(X).^2.*sin(X).^2.*sin(Y).^4)./3)./(((((cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).*(cos(X).^2.*cos(Y).^2-cos(X).^2.*sin(X).^2+cos(Y).^2.*sin(X).^2+cos(X).^2.*cos(Y).^4.*sin(X).^2+2.*cos(X).^2.*sin(X).^2.*sin(Y).^2-cos(Y).^2.*sin(X).^2.*sin(X).^2-cos(X).^2.*sin(X).^2.*sin(Y).^4))./6+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^3./27+(cos(X).^2.*cos(Y).^2.*sin(X).^2)./2-(cos(X).^2.*cos(Y).^6.*sin(X).^2)./2-(cos(X).^2.*cos(Y).^2.*sin(X).^2.*sin(Y).^2)./2-cos(X).^2.*cos(Y).^4.*sin(X).^2.*sin(Y).^2).^2-((cos(X).^2.*cos(Y).^2)./3-(cos(X).^2.*sin(X).^2)./3+(cos(Y).^2.*sin(X).^2)./3+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^2./9+(cos(X).^2.*cos(Y).^4.*sin(X).^2)./3+(2.*cos(X).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(Y).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(X).^2.*sin(X).^2.*sin(Y).^4)./3).^3).^(1/2)-((cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).*(cos(X).^2.*cos(Y).^2-cos(X).^2.*sin(X).^2+cos(Y).^2.*sin(X)^2+cos(X).^2.*cos(Y).^4.*sin(X).^2+2.*cos(X).^2.*sin(X).^2.*sin(Y).^2-cos(Y).^2.*sin(X).^2.*sin(Y).^2-cos(X).^2.*sin(X).^2.*sin(Y).^4))./6-(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^3./27-(cos(X).^2.*cos(Y).^2.*sin(X).^2)./2+(cos(X).^2.*cos(Y).^6.*sin(X).^2)./2+(cos(X).^2.*cos(Y).^2.*sin(X).^2.*sin(Y).^2)./2+cos(X).^2.*cos(Y).^4.*sin(X).^2.*sin(Y).^2).^(1/3)-(cos(X).^2.*sin(Y).^2)./3-(sin(X).^2.*sin(Y).^2)./3;

figure(1);surf(X,Y,abs(H))

figure(2);surf(X,Y,angle(H))

.

if you find this answer useful would you please be so kind to consider marking my answer as Accepted Answer?

To any other reader, if you find this answer useful please consider clicking on the thumbs-up vote link

thanks in advance for time and attention

John BG

<mailto:[e-mail] [e-mail]>

[John BG]

Thanks Dikra

this is John BG <mailto:[e-mail] [e-mail]>

if you capture the handles returned by function surf, for instance with:

figure(1);h_abs=surf(X,Y,abs(H));
figure(2);h_ang=surf(X,Y,angle(H));

then you can read the resulting surface point directly

Habs_x=h_abs.XData
Habs_y=h_abs.YData
Habas_z=h_abs.ZData

Hang_x=h_ang.XData
Hang_y=h_ang.YData
Hang_z=h_ang.ZData

also it is possible to change surface and edges transparency. If the surface is too dark, sometimes it's because of the high density of edges really close each other. Then the common practice is:

h_abs.EdgeColor='none'  % horse seat
h_ang.EdgeColor='none'  % pickeman helmet

[Dikra dikra]

Thank you. You are right. This helped me

Answer 2

[Star Strider]

Your code runs for me without error.

A more efficient approach would be:

theta5=[0:0.2:pi];
theta4=[0:0.2:pi];

[X,Y]=meshgrid(theta4,theta5);
H = cos(X).*sin(Y);

surf(Y,X,H)

[Dikra dikra]

Thank you. I'm grateful. the code runs without error .

But if i change the equation i get the same error, my new equation is :

clc

theta5=[0:0.1:pi];

theta4=[0:0.1:pi];

[X,Y]=meshgrid(theta4,theta5);

H=(((((cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).*(cos(X).^2.*cos(Y).^2-cos(X).^2*sin(X).^2+cos(Y).^2.*sin(X).^2+cos(X).^2.*cos(Y).^4.*sin(X).^2+2*cos(X).^2.*sin(X).^2.*sin(Y).^2-cos(Y).^2.*sin(X).^2.*sin(Y).^2-cos(X).^2.*sin(X).^2.*sin(Y).^4))./6+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^3./27+(cos(X).^2.*cos(Y).^2.*sin(X).^2)./2-(cos(X).^2.*cos(Y).^6.*sin(X).^2)./2-(cos(X).^2.*cos(Y).^2.*sin(X).^2.*sin(Y).^2)./2-cos(X).^2.*cos(Y).^4.*sin(X).^2.*sin(Y).^2).^2-((cos(X).^2.*cos(Y).^2)./3-(cos(X).^2.*sin(X).^2)./3+(cos(Y).^2.*sin(X).^2)./3+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(X).^2+sin(X).^2.*sin(Y).^2).^2./9+(cos(X).^2*cos(Y).^4.*sin(X).^2)./3+(2.*cos(X).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(Y).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(X).^2.*sin(X).^2.*sin(Y).^4)./3).^3).^(1/2)-((cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).*(cos(X).^2.*cos(Y).^2-cos(X).^2.*sin(X).^2+cos(Y).^2.*sin(X).^2+cos(X).^2.*cos(Y).^4.*sin(X).^2+2.*cos(X).^2.*sin(X).^2.*sin(Y).^2-cos(Y).^2.*sin(X).^2.*sin(Y).^2-cos(X).^2.*sin(X).^2.*sin(Y).^4))./6-(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^3./27-(cos(X).^2.*cos(Y).^2.*sin(X).^2)./2+(cos(X).^2.*cos(Y).^6.*sin(X).^2)./2+(cos(X).^2.*cos(Y).^2.*sin(X).^2.*sin(Y).^2)./2+cos(X).^2.*cos(Y).^4.*sin(X).^2.*sin(Y).^2).^(1/3)+cos(X).^2./3-cos(Y).^2./3+sin(X).^2./3+((cos(X).^2.*cos(Y).^2)./3-(cos(X).^2.*sin(X).^2)./3+(cos(Y).^2.*sin(X).^2)./3+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^2./9+(cos(X).^2.*cos(Y).^4.*sin(X).^2)./3+(2*cos(X).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(Y).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(X).^2.*sin(X).^2.*sin(Y).^4)./3)./(((((cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).*(cos(X).^2.*cos(Y).^2-cos(X).^2.*sin(X).^2+cos(Y).^2.*sin(X).^2+cos(X).^2.*cos(Y).^4.*sin(X).^2+2.*cos(X).^2.*sin(X).^2.*sin(Y).^2-cos(Y).^2.*sin(X).^2.*sin(X).^2-cos(X).^2.*sin(X).^2.*sin(Y).^4))./6+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^3./27+(cos(X).^2.*cos(Y).^2.*sin(X).^2)./2-(cos(X).^2.*cos(Y).^6.*sin(X).^2)./2-(cos(X).^2.*cos(Y).^2.*sin(X).^2.*sin(Y).^2)./2-cos(X).^2.*cos(Y).^4.*sin(X).^2.*sin(Y).^2).^2-((cos(X).^2.*cos(Y).^2)./3-(cos(X).^2.*sin(X).^2)./3+(cos(Y).^2.*sin(X).^2)./3+(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^2./9+(cos(X).^2.*cos(Y).^4.*sin(X).^2)./3+(2.*cos(X).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(Y).^2.*sin(X).^2.*sin(Y).^2)./3-(cos(X).^2.*sin(X).^2.*sin(Y).^4)./3).^3).^(1/2)-((cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).*(cos(X).^2.*cos(Y).^2-cos(X).^2.*sin(X).^2+cos(Y).^2.*sin(X)^2+cos(X).^2.*cos(Y).^4.*sin(X).^2+2.*cos(X).^2.*sin(X).^2.*sin(Y).^2-cos(Y).^2.*sin(X).^2.*sin(Y).^2-cos(X).^2.*sin(X).^2.*sin(Y).^4))./6-(cos(Y).^2-cos(X).^2-sin(X).^2+cos(X).^2.*sin(Y).^2+sin(X).^2.*sin(Y).^2).^3./27-(cos(X).^2.*cos(Y).^2.*sin(X).^2)./2+(cos(X).^2.*cos(Y).^6.*sin(X).^2)./2+(cos(X).^2.*cos(Y).^2.*sin(X).^2.*sin(Y).^2)./2+cos(X).^2.*cos(Y).^4.*sin(X).^2.*sin(Y).^2).^(1/3)-(cos(X).^2.*sin(Y).^2)./3-(sin(X).^2.*sin(Y).^2)./3;

surf(Y,X,H)

[Star Strider]

You have at least one term where some combination of your trigonometric functions is raised to the (1/3) power.

To illustrate the effect, run this:

x = 0:0.8:pi;
A = sin(x).^(1/3)
B = cos(x).^(1/3)

Any negative value raised to a non-integer power will be complex.

You must resolve this, since I do not know what you are doing.

[John BG]

Hi

this is John BG <mailto:[e-mail] [e-mail]>

there's nothing wrong with the .^ operator applied to negative values, it will work ok and return complex results.

The one that doesn't take complex values is SURF thus returning error when attempting so.

Please check my answer, thanks in advance.

Regards

John BG

<mailto:[e-mail] [e-mail]>

[Star Strider]

... with a completely irrelevant Comment!

[John BG]

it's not the power that causes error but attempting to push in a complex in SURF. My comment points at the fact that it's SURF and not the power the source of error, attempting a real only function with complex inputs.

[Jan]

The contentual repeating an irrelevant comment does not increase its relevance.

[Star Strider]

@Jan — Thank you!

[Dikra dikra]

Thank you

[Star Strider]

Noted.

The accepted Answer does not solve your original problem. You need to address the reason your function is taking non-integer powers of negative results, and describe what you actually want to do.

[Carlos Guerrero García]

The line defining H is too long for me, but the error detected by Star Strider (my +1 for StarStrider) can be solved using the "nthroot" command, and so, my suggestion for

x = 0:0.8:pi;
A = sin(x).^(1/3)

A = 1×4

0 0.8952 0.9999 0.8774

B = cos(x).^(1/3)

B = 
   1.0000 + 0.0000i   0.8865 + 0.0000i   0.1540 + 0.2667i   0.4517 + 0.7824i

is

x = 0:0.8:pi;
A = nthroot(sin(x),3)

A = 1×4

0 0.8952 0.9999 0.8774

B = nthroot(cos(x),3)

B = 1×4

1.0000 0.8865 -0.3079 -0.9034

Perhaps the same idea will be useful, but perhaps another way to plot that surface must be consider (perhaps as an implicit surface, but I don't know about how the parametrization appears). Also note that real(cos(1.6)^(1/3)), imag(cos(1.6)^(1/3)) and nthroot(cos(1.6),3) are not the same