why is my plot shows nothing?
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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');
采纳的回答
John D'Errico
2018-3-18
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.
更多回答（2 个）
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.
Rik
2018-3-18
2 个投票
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?
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