Thread Subject: Error :"In an assignment A(I) = B, the number of elements in B and I must be the same."

I have a problem with calculating Ep(I). Any suggestion how to sole this problem?

clear all;

% element numbers N, wavenumber B
N = input ('Enter the Number of Array Elements : ') ; 
lambda = input ('Enter the Value of Lambda (c/f) : ') ;
B =(2*pi/lambda);

% Magnitude, Phase, X,Y,Z coordinate
for I = 1 : N 
    Current = I
    An(I) = input ('Enter the Magnitude of the Current : ') ; 
    Jp(I) = input ('Enter the Phase of the Current : ') ;
    Xn(I) = input ('Enter the Position of Element on X-axis : ') ;
    Yn(I) = input ('Enter the Position of Element on Y-axis : ') ;
    Zn(I) = input ('Enter the Position of Element on Z-axis : ') ;
end

%azimut--> 0<Phi<360, elevation--> 0<Theta<180
Phhi = (0:1:360)*2*pi/180;
Thheta = (0:1:180)*2*pi/180;
[PHI,THETA] = meshgrid(Phhi,Thheta);

%R=[];
% calculate the array factor  
for I = 1:N      
    Ep(I)= B.*((Xn(I).*cos(PHI).*sin(THETA))+(Yn(I).*sin(THETA).*sin(PHI))+(Zn(I).*cos(THETA)));
    R(I)= An(I).*exp(1i.*(Ep(I)+(Jp(I).*pi/180)));
end

h(THETA,PHI) = sum(R);
AF(THETA,PHI) = abs(h(THETA,PHI));

%plot the array factor
X = AF.*sin(THETA).*cos(PHI);
Y = AF.*sin(THETA).*sin(PHI);
Z = AF.*cos(THETA);

figure(2);
mesh(X,Y,Z); %display
%surf(X,Y,Z) %colored faces

Best regards, Tadej

[Walter Roberson]

See also this earlier question on the same topic:

http://www.mathworks.com/matlabcentral/answers/14772-antenna-array-pattern-in-3d-space

[Tadej]

I tried to change Ep(I) with Ep(:,I) or Ep(I,:), but the error was still there.

Answer 1

[Walter Roberson]

I already described to you before why you are getting this error: you are trying to fit a vector or higher dimensional data in to the scalar Ep. At the time I pointed out which variables were vectors. You should be able to calculate from that analysis what size and shape of value is being calculated in each iteration of the loop. When you ran in to problems last time, you should have used

dbstop if error

and then run your code, and when it stopped running, used size() to examine the size and shape of the inputs and used size() of the expression on the right hand side to figure out what size and shape the left hand side must be.

Hint: re-read the tags you gave to this question. How can you hope to achieve those goals by calculating scalar results?

[Tadej]

Thank you Walter for this extensive reply.

[Tadej]

Thank you Walter. Now I do not have problems with calculating Ep(I) and R(I) thanks to you. There is a problem with plotting, but I will do my best to solve this problem.

clear all;

dbstop if error

% element numbers N, wavenumber B

N = input ('Enter the Number of Array Elements : ') ;

lambda = input ('Enter the Value of Lambda (c/f) : ') ;

B =(2*pi/lambda);

% Magnitude, Phase, X,Y,Z coordinate

for I = 1 : N

Current = I

An(I) = input ('Enter the Magnitude of the Current Element : ') ;

Jp(I) = input ('Enter the Phase of the Current Element : ') ;

Xn(I) = input ('Enter the Position of Current Element on X-axis : ') ;

Yn(I) = input ('Enter the Position of Current Element on Y-axis : ') ;

Zn(I) = input ('Enter the Position of Current Element on Z-axis : ') ;

end

% calculate the array factor

for PHI = 1:360

% change degree to radian

deg2rad(PHI) = (PHI*pi)/180;

for THETA = 1:180

% change degree to radian

deg2rad(THETA) = (THETA*pi)/180;

for I = 1:N

C(I) = Xn(I).*sin(deg2rad(THETA)).*cos(deg2rad(PHI));

D(I) = Yn(I).*sin(deg2rad(THETA)).*sin(deg2rad(PHI));

E(I) = Zn(I).*cos(deg2rad(THETA));

Ep(I) = B.*(C(I)+D(I)+E(I));

R(I)= An(I).*exp(1i.*(Ep (I) +(Jp(I).*pi/180)));

end

end

end

h(PHI,THETA) = sum(R);

AF(PHI,THETA) = abs(h(PHI,THETA));

%azimut--> 0<Phi<360, elevation--> 0<Theta<180

Phhi = (0:1:360)*pi/180;

Thheta = (0:1:180)*pi/180;

[PHI,THETA] = meshgrid(Phhi,Thheta);

%plot the array factor

X = AF.*sin(THETA).*cos(PHI);

Y = AF.*sin(THETA).*sin(PHI);

Z = AF.*cos(THETA);

figure(2);

mesh(X,Y,Z); %display

%surf(X,Y,Z) %colored faces

dbstop quit

Best regards, Tadej

[Tadej]

??? Error using ==> times

Matrix dimensions must agree.

Error in ==> Array3Dex7 at 70

X = AF.*sin(THETA).*cos(PHI);

I know that dimensions are not the same.

AF--> 360x180 double

PHI--> 181x361 double

THETA--> 181x361 double

How can I adjust dimension of AF?

[Walter Roberson]

When you are calculating AF, you run PHI and THETA from 1 to something. But then you define PHI and THETA through a meshgrid() call that starts the angles at 0 instead of at 1. You thus get a size mismatch. The obvious cure is to change your meshgrid() to start at 1 instead of 0.

[Tadej]

Thank you Walter. You are very helpful to me.

I have another question. I noticed that all 3D plots are made by using meshgrid function before AF function in my case. In my case I am able to get rid off 2xfor loops. But now I have a problem with calculating C(I). But if we look code above, this problem was not present. Do you maybe know what is the case?

code:

clear all;

dbstop if error

% element numbers N, wavenumber B

N = input ('Enter the Number of Array Elements : ') ;

lambda = input ('Enter the Value of Lambda (c/f) : ') ;

B =(2*pi/lambda);

% Magnitude, Phase, X,Y,Z coordinate

for I = 1 : N

Current = I

An(I) = input ('Enter the Magnitude of the Current Element : ') ;

Jp(I) = input ('Enter the Phase of the Current Element : ') ;

Xn(I) = input ('Enter the Position of Current Element on X-axis : ') ;

Yn(I) = input ('Enter the Position of Current Element on Y-axis : ') ;

Zn(I) = input ('Enter the Position of Current Element on Z-axis : ') ;

end

%azimut--> 0<Phi<360, elevation--> 0<Theta<180

Phi = (1:1:360)*pi/180;

Theta = (1:1:180)*pi/180;

[THETA,PHI] = meshgrid(Theta,Phi);

% calculate the array factor

for I = 1:N

C(I) = Xn(I).*sin(THETA).*cos(PHI);

D(I) = Yn(I).*sin(THETA).*sin(PHI);

E(I) = Zn(I).*cos(THETA);

Ep(I) = B.*(C(I)+D(I)+E(I));

R(I)= An(I).*exp(1i.*(Ep(I) +(Jp(I).*pi/180)));

end

h(PHI, THETA) = abs(sum(R));

AF(PHI, THETA) = abs(h(PHI, THETA));

%plot the array factor

X = AF.*sin(THETA).*cos(PHI);

Y = AF.*sin(THETA).*sin(PHI);

Z = AF.*cos(THETA);

figure(1);

mesh(X,Y,Z); %display

surf(X,Y,Z) %colored faces

Thank you in advance.

Greetings, Tadej

[Tadej]

C(I):

meshgrid() function befor AF() function

C(I) = Xn(I).*sin(THETA).*cos(PHI);

Xn(I)--> 1x2 double

PHI--> 360x180 double

THETA--> 360x180 double

meshgrid() function after AF() lunction

C(I) = Xn(I).*sin(deg2rad(THETA)).*cos(deg2rad(PHI));

Xn(I)--> 1x2 double

PHI--> 180x360 double

THETA--> 180x360 double

Answer 2

[Tadej]

Walter, could you please help me and tell me what is wrong with my code?

%Tadej Trinko; three-dimensional antenna array pattern
%email:[e-mail]
%Jožef Štefan International Postgraduate School (MPS IJS), Ljubljana,
%Slovenia

clear all;
close all
dbstop if error

V1=0; A1=0; C=0;
V2=0; A2=0; D=0;
V3=0; A3=0; E=0;

Ep=0; AnI=0; JpI=0;
R=0;

% element numbers N, wavenumber B
N = 3; %Number of elemnts in array
B = 0.14;   %B =(2*pi/lambda), wavenumber

% Magnitude, Phase, X,Y,Z coordinate
An = [2 2 2]; %Magnitude of 1st, 2nd and 3rd element
Jp = [120 90 60]; %Phase of 1st, 2nd and 3rd element
Xn = [1 2 3]; % Position of 1st, 2nd and 3rd element on X-axis
Yn = [1 2 3]; % Position of 1st, 2nd and 3rd element on Y-axis
Zn = [1 2 3]; % Position of 1st, 2nd and 3rd element on Z-axis

%azimut--> 0<Phi<360, elevation--> 0<Theta<180
Phi = (1:1:360)*pi/180; %azimuth
Theta = (1:1:180)*pi/180; %elevation
[THETA,PHI] = meshgrid(Theta,Phi);

% calculate the array factor 
%size(THETA)
%length(THETA)

%convert vector into matrix     C = Xn .* sin(THETA) .* cos(PHI);
V1 = repmat(Xn,360,60);
A1 = sin(THETA) .* cos(PHI);
C = A1.*V1;

%convert vector into matrix     D = Yn * sin(THETA) * sin(PHI);
V2 = repmat(Yn,360,60);
A2 = sin(THETA) .* sin(PHI);
D = A2.*V2;

%convert vector into matrix       E = Zn * cos(THETA);
V3 = repmat(Zn,360,60);
A3 = cos(THETA);
E = A3.*V3;

Ep = B.*(C+D+E);

%convert degree to radian
Jp = (Jp.*pi)/180;

%convert vector An, Jp into martix 
AnI = repmat(An,360,60);
JpI = repmat(Jp,360,60);

R = AnI.*exp(1i.*(Ep + JpI)); %Equation for array factor

%h(PHI, THETA) = R;
%AF(PHI, THETA) = abs(h(PHI, THETA));

%plot the array factor
X = R.*sin(THETA).*cos(PHI); 
Y = R.*sin(THETA).*sin(PHI);
Z = R.*cos(THETA);

figure();  
mesh(X,Y,Z); %display
surf(X,Y,Z) %colored faces

Best regards, Tadej