A simple issue with legend

2023 11 17
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更新时间：2023 11 17
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Hello,
I have a really simple question. To my surprise, I am could not help it (I have no idea !!!). When I type
x1=linspace(0,2*pi,1000);y1=sin(x1);y2=cos(x1);h1=plot(x1,y1,'-k');hold on;
plot(x1,0.*x1,'-k');hold on;h2=plot(x1,y2,'-k');legend([h1 h2],{'a','b'});
Then I get the following error message
Invalid argument. Type 'help legend' for more information.
I tried legend([h1 h2],['a','b']); which also does not work.
Sorry to bother you for this, thanks in advance!

5 个评论
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Dyuman Joshi
Dyuman Joshi 2023-11-17
Ran in:
Ran in:
It's working here in R2023b and in my R2021b as well.
Which MATLAB version are you working with?
x1=linspace(0,2*pi,1000);
y1=sin(x1);
y2=cos(x1);
h1=plot(x1,y1,'-r');
hold on;
plot(x1,0.*x1,'-k');
hold on;
h2=plot(x1,y2,'-b');
legend([h1 h2],{'a','b'});
Thanks for your respopnse!
I am using MATLAB 2023a. I really expect this version of MATLAB not have have any problem with this.
I lost a lot of time for this this morning. Do you knw an alternative way which works in MATLAB 2023a?
Dyuman Joshi
Dyuman Joshi 2023-11-17
That should work in R2023a.
For which line do you get the error?
Also, please copy and paste the full error message (i.e. all of the red text), if you have not already.
I do not know but when I used your code lines it works. I hues perhaps I forgot to use 'hold on', so maybe the error message is not about legend.
Thanks a lot!
Hello Star, Thanks.
Dyuman solved the problem. I explain the problem. If you type
x1=linspace(0,2*pi,1000);y1=sin(x1);y2=cos(x1);h1=plot(x1,y1,'-k');h2=plot(x1,y2,'-k');legend([h1 h2],'a','b');
then you get the following error message:
Error using legend
Invalid argument. Type 'help legend' for more information.
The problem has nothing to do with 'legend'. The problem is that after the first plot, I forgot to add 'hold on'. But, since the error message was very irrelevant I got confused.
Thanks a lot!

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