plotting complex exponential function

Question

yann mushid mushid 2023-1-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1897345-plotting-complex-exponential-function

评论： Walter Roberson 2023-1-20

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f=(0:10000);

d=(0.0075:0.03);

w=2*pi*f;

t=(0:0.2);

k=(81.6*pi);

rin=0.71;

%x=rin*exp(-1i*2*k*d);

y=0.71*exp(-1i*2*k*d);

d=abs(y);

plot(real(d),imag(y));

xlabel("thickness",'fontsize',10);

ylabel("rin",'FontSize', 10);

title("Input reflection coefficient as a function of the physical thickness 𝜆 ⁄ 8≤ 𝑑 ≤ 𝜆⁄2 ","fontsize",6);

grid on;

here is my code but when i try to run it it work but i dont gate any sygnal on de graphe the graph are just empty

i dont understant it please some one can help me or explain at the place i dit a wrong code

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Answer 1

Walter Roberson 2023-1-20

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https://ww2.mathworks.cn/matlabcentral/answers/1897345-plotting-complex-exponential-function#answer_1152420

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d=(0.0075:0.03);
w=2*pi*f;
t=(0:0.2);

The default increment for the : operator is 1, so you are programming

d=(0.0075:1:0.03);
w=2*pi*f;
t=(0:1:0.2);

but 0.0075+1 > 0.03 so d will only have a single entry, and 0+1 > 0.2 so t will only have a single entry.

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yann mushid mushid 2023-1-20

i try but it doesn't change anything i get the same result

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Answer 2

Walter Roberson 2023-1-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1897345-plotting-complex-exponential-function#answer_1152425

在 MATLAB Online 中打开

Removing the variables that you do not use, and setting a finer increment for d

d=(0.0075:0.001:0.03);

k=(81.6*pi);

y=0.71*exp(-1i*2*k*d);

plot(real(y),imag(y));

xlabel("thickness",'fontsize',10);

ylabel("rin",'FontSize', 10);

title("Input reflection coefficient as a function of the physical thickness 𝜆 ⁄ 8≤ 𝑑 ≤ 𝜆⁄2 ","fontsize",6);

grid on;

You were taking real(abs(y)) as your independent coordinate, but real(abs(y)) is constant

syms D

Y=0.71*exp(-1i*2*k*D);

abs(Y)

ans =

but D is real so imag(D) is 0, so abs(Y) is the constant 71/100

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yann mushid mushid 2023-1-20

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hook thank you

so if i plot this auther code is ti normal to gate a line or they are same mistake on my code?

f=(0:10);
t=(0:0.1);
w=2*pi*f;
rin=0.71;
%y=rin*exp(*-1i*w*t);
y=0.71*exp(-1i*w*t);
%rin=abs(y);
plot(real(f),imag(y));

Walter Roberson 2023-1-20

在 MATLAB Online 中打开

t=(0:0.1);

That means you want to construct the list of numbers that starts with 0, and increases by 1 each time, and ends no later than 0.1 . That list describes only a single number.

Your f values are all integers and 2*pi*integer is a full sine or cosine cycle, so *exp(-1i*w*t) will have 0 imaginary part anywhere that t is an integer. But there is only 1 t value and it is an integer, so imag(y) is going to be 0 at that one location.

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