How to plot step functions in Matlab

Question

Sangani Prithvi 2020-10-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/631999-how-to-plot-step-functions-in-matlab

评论： VBBV 2020-10-31

采纳的回答： VBBV

I have a function involving

y=o for x<o;

y=exp(-x)*cos(x) for 0<x<2pi();

y=2*exp(-x)*cos(x) for x>2pi();

please help me to plot such a type of function in xy space

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Answer 1

VBBV 2020-10-31

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https://ww2.mathworks.cn/matlabcentral/answers/631999-how-to-plot-step-functions-in-matlab#answer_529809

编辑：VBBV 2020-10-31

在 MATLAB Online 中打开

%if true
  % code
%end
x = -2*pi:0.1:3*pi;
for i = 1:length(x);
if x(i)<0;
y(i)=0;
elseif x(i)<=2*pi & x(i)>=0 ;
y(i) = exp(-x(i))*cos(x(i)*pi/180);
elseif x(i) > 2*pi ;
y(i) = 100*exp(-x(i))*cos(x(i)*pi/180);
end;
end;
plot(x,y)
axis([-2*pi 3*pi -0.2 1])

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Sangani Prithvi 2020-10-31

y(i) = 100*exp(-x(i))*cos(x(i)*pi/180

can you please explain why did you mutliply with 100 in the above equation?

VBBV 2020-10-31

在 MATLAB Online 中打开

you can use a smaller number, say 2, but

y(i) = 2*exp(-x(i))*cos(x(i)*pi/180);

gives a very small step height compared to

y(i) = exp(-x(i))*cos(x(i)*pi/180)

So in the graph it is not noticeable clearly

Thats why i used to 100 which amplifies the step height.

Remember in both cases the step nature does not vary. i,e, decreasing exponential function according to your equations

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Answer 2

Vladimir Sovkov 2020-10-31

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/631999-how-to-plot-step-functions-in-matlab#answer_529804

编辑：Vladimir Sovkov 2020-10-31

在 MATLAB Online 中打开

syms x;
y=piecewise(x<0,0, 0<=x<2*pi,exp(-x).*cos(x), x>=2*pi,2*exp(-x).*cos(x));
t=linspace(-pi,4*pi,1000);
plot(t,subs(y,x,t));

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Sangani Prithvi 2020-10-31

thank you

Vladimir Sovkov 2020-10-31

Welcome.

By the way, in the question, you did not specify what the function is equal to at the boundary points x=0 and x=2*pi; in the code I implied the right limit but you can easily alter this convention.

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