Why when I put legend for 3 functions it only shows 1 on the graph?

Question

Zhuoying Lin 2017-10-27

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/363554-why-when-i-put-legend-for-3-functions-it-only-shows-1-on-the-graph

评论： Zhuoying Lin 2017-10-27

Hi, below is my script:

x=linspace(0,2*pi,100);
y1=1-x.^2/factorial(2);
y2=y1+x.^4/factorial(4);
y3=cos(x);
plot(x,y1,'k:')
legend('2 terms approx')
hold on
plot(x,y2,'k--')
legend('3 terms approx')
hold on
plot(x,y3,'r')
legend('cos(x)')
xlabel('x')
ylabel('y')

Thanks!

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Answer 1

Birdman 2017-10-27

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https://ww2.mathworks.cn/matlabcentral/answers/363554-why-when-i-put-legend-for-3-functions-it-only-shows-1-on-the-graph#answer_288045

在 MATLAB Online 中打开

Try this:

legend('2 terms approx','3 terms approx','cos(x)')

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Zhuoying Lin 2017-10-27

Yes it works! Thanks for your soln and immediate response!

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Answer 2

Walter Roberson 2017-10-27

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/363554-why-when-i-put-legend-for-3-functions-it-only-shows-1-on-the-graph#answer_288047

在 MATLAB Online 中打开

legend() calls with text arguments never add the text to the existing legend entries.

As of R2017a, if there is a legend in effect and new graphics objects are added, then the legend is automatically expanded to include new entries; in versions up to R2016b, no entries were automatically added.

The entries that are automatically by default use names such as 'data1'. You can change this by adding a DisplayName property at the time the object was created. So, for example,

%R2017a or later
x=linspace(0,2*pi,100);
y1=1-x.^2/factorial(2);
y2=y1+x.^4/factorial(4);
y3=cos(x);
plot(x,y1,'k:', 'DisplayName', '2 terms approx');
hold on
plot(x,y2,'k--', 'DisplayName', '3 terms approx');
plot(x,y3,'r', 'DisplayName', 'cos(x)');
hold off
legend show
xlabel('x')
ylabel('y')

or

%R2016b or earlier
x=linspace(0,2*pi,100);
y1=1-x.^2/factorial(2);
y2=y1+x.^4/factorial(4);
y3=cos(x);
plot(x,y1,'k:')
legends{1} = '2 terms approx';
hold on
plot(x,y2,'k--')
legends{end+1} = '3 terms approx';
plot(x,y3,'r')
hold off
legends{end+1} = 'cos(x)';
legend(legends{:})
xlabel('x')
ylabel('y')