how to plot a periodic function fro negative to positive?

Question

Daniel Niu 2022-10-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1831298-how-to-plot-a-periodic-function-fro-negative-to-positive

评论： Sam Chak 2022-10-20

采纳的回答： Torsten

在 MATLAB Online 中打开

Dear friend,

How to plot a periodic function for example 2*x from negative to positive?

I know a method to plot periodic function using mod but, It seems can not plot the negative range.

t = 10; % total simulation time
T = 3; % period
x = 0:0.1:t;
% lets say your original function is y=2*x which repeated every T second, then
y = 2*(mod(x,T));
plot(x,y)

However, because the mod of negative is a little strange, I don't know how to modify the code.

Your help would be highly appreciated

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V Sairam Reddy 2022-10-20

Please check this MATLAB Answer

Daniel Niu 2022-10-20

Dear Mr Reddy,

The answer is not what I want. for example. I want my function at -pi:pi periodic. But the method only can plot function in 0:2pi.

I am looking forward to your reply.

Best regards.

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Answer 1

Torsten 2022-10-20

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https://ww2.mathworks.cn/matlabcentral/answers/1831298-how-to-plot-a-periodic-function-fro-negative-to-positive#answer_1079548

在 MATLAB Online 中打开

T = pi; % period

x = -10:0.1:10;

% lets say your original function is y=2*x which repeated every T second, then

y = 2*(mod(x-pi,2*pi)-pi);

plot(x,y)

grid on

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Daniel Niu 2022-10-20

Wow, thank you, Torsten

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Answer 2

Sam Chak 2022-10-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1831298-how-to-plot-a-periodic-function-fro-negative-to-positive#answer_1079523

编辑：Sam Chak 2022-10-20

在 MATLAB Online 中打开

Hi @Daniel Niu

Are you looking for this?

Edit: Made changes as per shown in your diagram. Because the amplitude is unknown, then you need to multiply the function by a certain factor to get the desired amplitude.

t = 3*pi; % total simulation time

T = 2*pi; % period (from -π to +π) --> π - (-π) = 2π

x = -t:0.01:t;

y = 2*(mod((x - pi), T)) - 2*T/2; % also need to shift x by pi

plot(x/pi, y), grid on,

xlabel('{$\frac{x}{\pi}$}', 'interpreter', 'latex', 'fontsize', 16)

ylabel('{$y$}', 'interpreter', 'latex', 'fontsize', 16)

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Daniel Niu 2022-10-20

Dear Mr Chak,

I am looking something like this.

Thank you so much for your answers.

Sam Chak 2022-10-20

Don't mention it @Daniel Niu. I have edited the code to display the sawtooh wave as per your sketched diagram. If you find the solution is helpful, please consider accepting ✔ and voting 👍 the Answer. Thanks!

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