Legend incorrect when plotting with quiver

Question

Dayne Filer 2017-9-12

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链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/356306-legend-incorrect-when-plotting-with-quiver

回答： Reece Teramoto 2017-9-15

I cannot get the legend to display as desired when plotting with quiver. I am using R2017a.

    % Some parameters
    k1 = 1;
    k2 = 1;
    k3 = 10;
    E = 10;
    % establish the grid of possible C and S values
    [cmesh,smesh] = meshgrid(0:0.5:10,0:0.5:10);
    % Calculate nullcine and the tendencies at each value of the grid
    cnull = k1.*E.*smesh./(k1.*smesh + k2 + k3);
    dsdt = -k1.*(E - cmesh).*smesh + k2.*cmesh; 
    dcdt = k1.*(E - cmesh).*smesh - (k2 + k3).*cmesh;
    % Plot the phase plane
    quiver(smesh,cmesh,dsdt,dcdt);
    hold on;
    plot(smesh, cnull);
    hold on;
    plot([1:10],[1:10]);
    legend('Trajectory', 'C nullcline', 'S(t),C(t)');
    xlabel('S');
    ylabel('C');
    axis([0,10,0,10]);
    title('Phase Plane');

The line colors do not match the plotted lines in the figure created.

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Answer 1

Reece Teramoto 2017-9-15

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/356306-legend-incorrect-when-plotting-with-quiver#answer_281718

在 MATLAB Online 中打开

Change this line:

plot(smesh, cnull);

to this:

plot(smesh(:,1), cnull(:,1));

Originally, since 'smesh' and 'cnull' are both 2-D matrices where each column is identical, you were plotting the same curve many times on top of each other with this one line of code, since you were using the 'plot' function with two matrices as inputs.

This caused many curves to be plotted on the figure, and the 'legend' command will pull the plots in chronological order unless otherwise specified.