How to plot a piecewise function?

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Alexandros Dhimas
Alexandros Dhimas 2016-12-20
评论： Walter Roberson 2020-12-25
  3 个评论
显示 1更早的评论
Stephen23
Stephen23 2020-12-25
Original question asked by Alexandros Dhimas on 20th December 2016 retrieved from Google Cache:
http://web.archive.org/web/20201225181844/https://webcache.googleusercontent.com/search?q=cache%3ASu-ZTnJ4_rMJ%3Ahttps%3A%2F%2Fwww.mathworks.com%2Fmatlabcentral%2Fanswers%2F317651-how-to-plot-a-polyclonal-expression-using-if-statement
How to plot a polyclonal expression using if statement?
Hello, I' ve got a polyclonal function to plot (using if statement) as shown on this picture:
for -5<x<30.
My thougth on the solution was:
x=linspace(-5,30,1000);
if x<0
y=10*x.^0;
else if x>=0 & x<9
y=10*x+10;
else if 9<=x
y=15*sqrt(4*x)+10;
end
end
end
plot(x,y)
But i get this on the command window "Error using plot A numeric or double convertible argument is expected"
I can't find any mistakes on my code.

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采纳的回答

Alexandros Dhimas
Alexandros Dhimas 2016-12-21
编辑：Alexandros Dhimas 2016-12-21
Solution usin if statement:
x=linspace(-5,30,1000);
for i=1:1000
if x(i)<0
y(i)=10;
elseif x(i)>=0 & x(i)<9
y(i)=10*x(i)+10;
else
y(i)=15*sqrt(4*x(i))+10;
end
end
plot(x,y)

更多回答（2 个）

Walter Roberson
Walter Roberson 2016-12-20
Either use a for loop or (better) use logical indexing. http://blogs.mathworks.com/steve/2008/01/28/logical-indexing/
Roger Stafford
Roger Stafford 2016-12-21
If you only want to plot the function, do this:
x1 = linspace(-5,0,50); y1 = 10*ones(1,50);
x2 = linspace(0,9,90); y2 = 10*x2+10;
x3 = linspace(9,30,210); y3 = 15*sqrt(4*x3)+10;
plot([x1,x2,x3],[y1,y2,y3])
Another way:
x = linspace(-5,30,400);
y = (x<0)*10+(x>=0&x<9).*(10*x+10)+(x>=9).*(15*sqrt(4*abs(x))+10);
plot(x,y)

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