# I want to plot graph when alpha =2.8 or 2.9, but the graph not appear.

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mohd akmal masud on 23 Mar 2023
Commented: mohd akmal masud on 27 Mar 2023
Dear Sir,
I want to plot the graph for alpha=2.8 or 2.9. But the graph not appear.
Anyone can help me
clc
clear all
close all
theetasd = -90:.01:90; %Defining X axis vector
theetaid = 30; %Variable Theeta i in degrees
phisd = 90;
theetai = theetaid * pi/180; %Variable Theeta i in radian
theetas = theetasd * pi/180; %Variable Theeta s in radian
phis = phisd * pi/180;
%constants
ay =1 ;
az= 1;
H0=1;
n=1;
eita=1;
y=1;
z=1;
%Parameters
lembda = 0.8;
beeta = 8;
a = 5*lembda;
b = 5*lembda;
d=1;
syms r
alpha=2.8
part1=-(j.*eita.*a.*b.*H0.*((pi./2).^0.5).*(beeta.*d.*cos(theetai)).^abs((3-alpha)/2).* besselh(abs((3-alpha)/2),1,(beeta.*d.*cos(theetai))).* beeta.*(2.^(3-alpha)).*((pi).^0.5)./2);
part2=(2.*(pi).*(gamma((alpha)./2)));
C=(part1)/(part2);
Ei = n.*H0.*((pi./2).^0.5).*((ay.*cos(theetai))+(az.*sin(theetai))).*(beeta.*z.*cos(theetai)).^abs((3-alpha)/2).*(exp(-j.*beeta.*((y.*sin(theetai))))).*besselh(abs((3-alpha)/2),1,(beeta.*d.*cos(theetai)));
%Equation for Es-Phi
p = beeta.*a./2.*(sin(theetas).*cos(phis));
q = beeta.*b./2.*((sin(phis).*sin(theetas))-sin(theetai));
Esth = (C.*exp(-j.*beeta.*r)./r.^(alpha-2)).*((cos(theetas)).*sin(phis).*(((sin(p)./(p)).*(sin(q))./(q))));
Esphi = (C.*exp(-j.*beeta.*r)./r.^(alpha-2)).*(cos(phis).*(((sin(p))./(p)).*(sin(q))./(q)));
%Equation for Es
Es=sqrt((Esth).^2+(Esphi).^2);
%Equation for Sigma
sigma = limit((4.*pi.*r.^2).*abs((Esth).^2/(Ei).^2), r, inf);
sigma = 5*log( sigma);
plot(theetasd,sigma,'black--')
the cyclist on 23 Mar 2023
I suggest that you learn to use the debugging tools that MATLAB provides. You can set a breakpoint at the plotting line, and see what is going on.
In this case, I can see that every value of sigma is Inf. I did not trace back why that happens.

Sandeep on 27 Mar 2023
Hi mohd akmal masud,
It is my understanding that you are facing an issue in plotting a Graph simulating Electromagnetic wave propagation. The reason is that the sigma variable is a scalar value and cannot be plotted against a vector. In the last line of the code, sigma is assigned a scalar value by taking the logarithm of a limit expression. Therefore, when plot(theetasd, sigma, 'black--') is executed, MATLAB throws an error because it is not possible to plot a scalar value against a vector.
To fix this, you could modify the code to store the conductivity values for each value of theetasd in a vector, rather than just a single scalar value. You could initialize an empty vector sigma_vals and then assign the calculated sigma value to sigma_vals(i) at each iteration of the loop. Then, you can plot the resulting sigma_vals vector against theetasd.
For more insite on Plot function refer:
##### 2 CommentsShow 1 older commentHide 1 older comment
mohd akmal masud on 27 Mar 2023
Dear Sir @Sandeep,
Can you help me to adjust the coding then I can plot the graph?

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