why is my plot shows nothing?

why is my plot shows nothing?

syms w
  w=-1*10*pi:0.005:10*pi;
  plot(w,sqrt(w.^2+w.^6)/(1+w.^4),'b');

Answer 1

[John D'Errico]

Because you need to read the getting started tutorials for MATLAB? In 3 simple (truly basic) lines of code, I see 4 significant errors, some worse than others.

syms w

You do not need to define w as a sym, if you will then overwrite it with a double. So the syms reference is a waste of time. More importantly, it suggests that you do not understand how MATLAB works with variables, that the next line which assigns w completely ignores the previous use of syms for w. So this is an error of comprehension.

w=-1*10*pi:0.005:10*pi;

Use linspace here, NOT colon to create a vector. The final element will not be 10*pi if you use colon. -1*10*pi is also silly, since -10*pi is equivalent.

plot(sqrt(w,w.^2+w.^6)/(1+w.^4),'b');

Several problems in this last line, even though I cannot even guess what you are trying to write.

sqrt(w,w.^2+w.^6) is a meaningless expression. I cannot even guess what you want to do there.

You know enough to use the .^ operator when w is a vector. You also need to learn about the .* and ./ operators for vectors. They are equally valuable and equally important.

It is vaguely possible that you really wanted to write this:

plot(w,sqrt(w.^2+w.^6)./(1+w.^4),'b');

But that would be a complete and wild guess on my part, and I tend to be a poor guesser.

So it is time for you to read the documentation.

[geometry geometry]

Thanks! and sorry for my trivial mistakes; because I'm beginner in matlab.

Answer 2

[Birdman]

Replace

 plot(sqrt(w,w.^2+w.^6)/(1+w.^4),'b')

with

 plot(sqrt(w.^2+w.^6)./(1+w.^4),'b')

Also,

 syms w

line is irrelevant since in second line, you overwrite it with a numeric vector. Therefore delete it.

Answer 3

[Rik]

Because the command you are using has an incorrect syntax. You can't enter two input arguments to sqrt.

Also, you first declare w as a sym, but then overwrite it with a vector. You also didn't provide an x vector to plot (it is not strictly necessary, but it is good coding practice). And as a last remark, did you mean to use a matrix division inside that plot function?