# How can i plot a boundary line in contour plot

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Hello,
I have this code for ploting a contour plot.
%bare electron mass (kg)
a=1.855;
eb=-3.276;
ep=-1.979;
t=-1.844;
FS = 24; %label fontsize
FSN = 24; %number fontsize
LW = 2; %linewidth
% Change default axes fonts.
% set(0,'DefaultAxesFontName', 'Times New Roman');
% set(0,'DefaultAxesFontSize', FSN);
% Change default text fonts.
% set(0,'DefaultTextFontname', 'Times New Roman');
% set(0,'DefaultTextFontSize', FSN);
hbarChar=['\fontname{MT Extra}h\fontname{Times New Roman}'];
iform = complex(0.0,1.0);
% Creating necessary k-vectors
kx = linspace(-1.4,1.4,500);
ky = linspace(-2,2,500);
[k_x,k_y] = meshgrid(kx, ky);
phi=exp(-iform.*k_x*a)+2.*exp(iform.*k_x*a/2).*cos(sqrt(3).*k_y.*a/2);
figure (2)
energy_mesh1 = (eb+ep)/2+sqrt(((eb-ep)/2)^2+t^2.*phi.*conj(phi)) ;
energy_mesh2 = (eb+ep)/2-sqrt(((eb-ep)/2)^2+t^2.*phi.*conj(phi));
g=energy_mesh1-energy_mesh2;
contour(k_x,k_y,g,500,'LineWidth',1.5)
colormap('jet');
I want to connect dark points of the contour plot.
What should I do?
##### 5 个评论显示隐藏 4更早的评论
I have the same question as @Wan Ji. What are the dark points (your image didn't help) and how do you want to connect them? With lines? Perhaps an illustration would help.

### 采纳的回答

Copy of original code with the following changes.
• contour(k_x,k_y,g,500) chaanged to contour(k_x,k_y,real(g),500)
• Commented-out changes to default font properties
%bare electron mass (kg)
a=1.855;
eb=-3.276;
ep=-1.979;
t=-1.844;
FS = 24; %label fontsize
FSN = 24; %number fontsize
LW = 2; %linewidth
% Change default axes fonts.
% set(0,'DefaultAxesFontName', 'Times New Roman');
% set(0,'DefaultAxesFontSize', FSN);
% Change default text fonts.
% set(0,'DefaultTextFontname', 'Times New Roman');
% set(0,'DefaultTextFontSize', FSN);
hbarChar=['\fontname{MT Extra}h\fontname{Times New Roman}'];
iform = complex(0.0,1.0);
% Creating necessary k-vectors
kx = linspace(-1.4,1.4,500);
ky = linspace(-2,2,500);
[k_x,k_y] = meshgrid(kx, ky);
phi=exp(-iform.*k_x*a)+2.*exp(iform.*k_x*a/2).*cos(sqrt(3).*k_y.*a/2);
figure (2)
energy_mesh1 = (eb+ep)/2+sqrt(((eb-ep)/2)^2+t^2.*phi.*conj(phi)) ;
energy_mesh2 = (eb+ep)/2-sqrt(((eb-ep)/2)^2+t^2.*phi.*conj(phi));
g=energy_mesh1-energy_mesh2;
contour(k_x,k_y,real(g),500)
colormap('jet');
Compute the location of lowest values excluding the image edges
% Get lowest points
idx = find(imregionalmax(-real(g)));
% Remove lowest points at edges
[row,col] = ind2sub(size(g),idx);
isEdge = row==1 | row==size(g,1) | col==1 | col==size(g,2);
idx(isEdge) = [];
Compute center and radius of circle
This assumes that the points will lie along the circumference of a circle. If the expected shape is oval, that's an easy change. If the expected shape is unknown, you'll need to sort the points so they are in order and then just plot their connections with a line or compute a polyshape.
% compute circle
xyLoc = [k_x(idx),k_y(idx)];
cnt = mean(xyLoc);
% Plot points and circle
axis equal
hold on
h = plot(k_x(idx),k_y(idx), '*w','MarkerSize', 14);
'Curvature',[1,1], 'EdgeColor', 'w');
Linear connections
First you have to sort the coordinates.
[th, ~] = cart2pol(xyLoc(:,1),xyLoc(:,2));
[~, sortIdx] = sort(th);
xyLocSort = xyLoc(sortIdx,:);
xyLocSort = [xyLocSort; xyLocSort(1,:)]; % wrap polygon
h = plot(xyLocSort(:,1), xyLocSort(:,2), 'w-'); ### Community Treasure Hunt

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