How can I plot a sin (x^2) function

Question

Drew Levis 2019-9-16

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https://ww2.mathworks.cn/matlabcentral/answers/480697-how-can-i-plot-a-sin-x-2-function

评论： DGM 2022-11-11

here is my code and it works but the figure is obviously not a sin(x^2) function from -pi to pi

syms x;
f=@(x)sin(x.^2);
x=[-pi pi];plot(x,f(x))
grid

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Ayed 2022-11-11

Convert Fahrenheit degrees to Celsius degrees!

DGM 2022-11-11

I have no idea why you decided to put this unrelated question here as an exclamation.

See the attached files.

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Answer 1

John D'Errico 2019-9-17

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https://ww2.mathworks.cn/matlabcentral/answers/480697-how-can-i-plot-a-sin-x-2-function#answer_392174

编辑：John D'Errico 2019-9-17

First, there is ABSOLUTELY NO reason to predefine x as a sym. So this line is completely irrelevant:

syms x;

When you do create x, you overwrite the symbolic version of x that you created before anyway.

Next, you created a function

f=@(x)sin(x.^2);

Good there. But then what?

What do you think this does?

x=[-pi pi];

It does NOT create the interval [-pi,pi]. Instead, it creates a vector of length 2, so TWO values, -pi and pi. Then when you plotted, using

plot(x,f(x))

it plots TWO points, connected with a straight line. And since the two poiints each had function value of zero, the line is perfectly horizontal. Compare that to this version:

f=@(x)sin(x.^2);
x=linspace(-pi,pi,100);
plot(x,f(x))
grid

See that I never needed to pre-define x as symbolic. (Why would you want to do that anyway? Just because you don't know the value of something, does not mean it must automatically be symbolic. This is perhaps the one of most common mistakes I see made by new users.)

Simpler yet, you might have done just this:

f = @(x) sin(x.^2);
fplot(f,[-pi,pi])
grid

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Drew Levis 2019-9-17

I appericate the help. I started to think and come to a simlar answer when looking at the figure again. I am glad my thoughts were confirmed. THANK YOU again.

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