plotting a special function

Question

Ali Roshanzamir 2020-8-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/574849-plotting-a-special-function

评论： Ali Roshanzamir 2020-8-4

Hey guys,

I want to plot this curve. Please help me. It's too important for me!

N=45;

N(θ)= N*7/8 for 0<θ<π/4 & π<θ<5π/4

-N/8 for other θ

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Ali Roshanzamir 2020-8-4

在 MATLAB Online 中打开

I did this but it doesn't show anything

N=45;
for teta=0:2*pi,
if((teta>pi/4)&(pi<teta<=5*pi/4)),
Nteta=7*N/8;
else
Nteta=-N/8;
end;
end;
subplot(2,1,1)
plot(teta,Nteta)

Walter Roberson 2020-8-4

Use logical indexing based upon logical comparisons you do between theta and the constants of the question.

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Answer 1

Walter Roberson 2020-8-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/574849-plotting-a-special-function#answer_474880

在 MATLAB Online 中打开

if((teta>pi/4)&(pi<teta<=5*pi/4)),
Nteta=7*N/8;

You are overwriting all of Nteta there, with a scalar. At the end of your for loop, Nteta will be a scalar that has whatever value was last assigned to it.

plot(teta,Nteta)

After the for teta loop, the loop control variable (teta) will have the value it was assigned last in the loop. So it will be the scalar 6. Then you are plotting that scalar on the x axis and the scalar Nteta on the y axis -- a single point. However, when you plot a single point without indicating a marker, then plot tries to draw just the between the single point and itself, which is not going to produce any visible marking.

for teta=0:2*pi,

Remember that the default increment for the : operator is 1, so you are asking to run the loop with teta = 0, 1, 2, 3, 4, 5, and 6.

I recommend that you read https://www.mathworks.com/matlabcentral/answers/534868-make-matrix-with-loop#answer_439778