Legend & Labeling points in a plot

Question

rezheen 2025-5-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2177353-legend-labeling-points-in-a-plot

评论： Matt J 2025-5-28

I'd like to have a legend that shows all tangent lines and curves of my graph, also label points if possible either in the legend or right next to the points themselves. My code doesn't do either currently:

syms a x

y=1/(x-1); m=-1; dy=diff(y);

x1_=subs(dy,a); eq=x1_==m; x1=solve(eq); y1=subs(y,x1);

line=m*(x-x1)+y1;

disp('The tangent line(s) are:')

The tangent line(s) are:

for k=1:length(x1)

fprintf('y = %s\n',char(line(k)))

f=plot(x1,y1,'.', 'color', 'black','markersize',15); hold on

g=fplot(line); set(g,'color','black','LineStyle', '--'); hold on;

end

y = - x - 1 y = 3 - x

h=fplot(y); set(h,'color','blue','Linewidth', 1);

j=xline(0); set(j,'color','black','Linewidth', 1.5)

k=yline(0); set(k,'color','black','Linewidth', 1.5)

xlabel('x'); ylabel('y'); title('Curve & tangent line & points')

legend([g h],{'Tangent line', 'Curve'})

Error using horzcat
Dimensions of arrays being concatenated are not consistent.

Thanks.

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Answer 1

Matt J 2025-5-28

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2177353-legend-labeling-points-in-a-plot#answer_1565546

编辑：Matt J 2025-5-28

在 MATLAB Online 中打开

syms a x

y=1/(x-1); m=-1; dy=diff(y);

x1_=subs(dy,a); eq=x1_==m; x1=solve(eq); y1=subs(y,x1);

line=m*(x-x1)+y1;

disp('The tangent line(s) are:')

The tangent line(s) are:

for k=1:length(x1)

fprintf('y = %s\n',char(line(k)))

f(k)=plot(x1(k),y1(k),'.', 'MarkerSize',15); hold on

g(k)=fplot(line(k),'--');

end

y = - x - 1 y = 3 - x

h=fplot(y,'color','blue','Linewidth', 1);

xline(0,'color','black','Linewidth', 1.5);

yline(0,'color','black','Linewidth', 1.5);

xlabel('x'); ylabel('y'); title('Curve & tangent line & points')

legend([g(:); f(:); h],{'Tangent line 1','Tangent line 2' ,'Point 1','Point 2', 'Curve'})

col={'red','green'};

[f.Color]=deal(col{:});

[g.Color]=deal(col{:});

hold off

●

6 个评论
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Matt J 2025-5-28

编辑：Matt J 2025-5-28

在 MATLAB Online 中打开

syms a x

y=1/(x-1); m=-1; dy=diff(y);

x1_=subs(dy,a); eq=x1_==m; x1=solve(eq); y1=subs(y,x1);

line=m*(x-x1)+y1;

disp('The tangent line(s) are:')

The tangent line(s) are:

disp(char(compose('y = %s',string(line))))

y = - x - 1 y = 3 - x

scatlabel( scatter(x1,y1,'k.', 'SizeData',150) ); hold on

g=fplot(line,'k--');

h=fplot(y,'color','blue','Linewidth', 1); hold off

xline(0,'color','black','Linewidth', 1.5);

yline(0,'color','black','Linewidth', 1.5);

xlabel('x'); ylabel('y'); title('Curve & tangent line & points')

legend([g(1); h],{'Tangent line', 'Curve'})

function varargout=scatlabel(H,labels)

%Add labels to the (XData,YData,ZData) coordinates in a plot pointed to by a

%graphics handle object H.

%

% Hout=scatlabel(H) %Labels will be simple enumeration

% Hout=scatlabel(H,labels) %Provided labels can be string or numeric

%

%Hout is a handle to a GraphPlot object containing the labels.

ax=H(1).Parent;

S.XData=[H.XData];

S.YData=[H.YData];

for i=numel(H):-1:1

if isprop(H(i),'ZData') && ~isempty(H(i).ZData),

ZData{i}=[H(i).ZData];

else

ZData{i}=zeros(1,numel(H(i).XData));

end

S.ZData=cell2mat(ZData);

N=numel(S.XData);

if nargin<2, labels=1:N; end

assert(numel(labels)==N,'Number of labels doesn''t match number of data points');

tf=ishold;

if ~tf

hold(ax,'on')

end

args={'Marker','none','NodeLabel',labels,'NodeFontSize',12,'HitTest','off',...

'XData', S.XData, 'YData', S.YData};

if isfield(S,'ZData'),

args=[args,{'ZData',S.ZData}];

end

H=plot(ax,graph( speye(N),'omit' ),args{:});

if ~tf

hold(ax,'off')

end

if nargout, varargout={H}; end

end

rezheen 2025-5-28

That's great! But instead of labeling the points '1', '2', could it label what they actually are?

In this case (0, -1), (2, 1)

Matt J 2025-5-28

在 MATLAB Online 中打开

Yes, you can provide whatever labels you want. From the help doc,

% Hout=scatlabel(H,labels) %Provided labels can be string or numeric

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Legend & Labeling points in a plot

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