MATLAB: Plotting concentric circles using contour

plotting

I'm trying to plot a few concentric circles with the following codes, but what I get is an ellipse, i don't know why:

[x,y] = meshgrid(-3:0.1:3,-3:0.1:3);
z = x.^2+y.^2;
contour(x,y,z)

Best Answer

Use the axis function, specifically either:

axis('equal')                           % Function Expression

or:

axis equal                              % Command Expression

Related Solutions

MATLAB: Add contours to scatter3 plot

Contours can be drawn on a 2D slice in a 3D figure using contourslice.

I'm not sure what the contours are that you want to plot. I just specify some random contour in variable V.

Note that you are not projecting points at the wall, but at the location of the maximum. I fixed this by actually plotting at the limits.

x = mvnrnd(1, 3, 100);
y = mvnrnd(2, 3, 100);
z = mvnrnd(3, 3, 100);
scatter3 (x, y, z, 'filled')
hold on
xl = xlim;
yl = ylim;
zl = zlim;
xlim(xl); ylim(yl); zlim(zl); % fix the limits for if we rotate
scatter3 (0*x+xl(2), y, z, '.')
scatter3 (x, 0*y+yl(2), z, '.')
scatter3 (x, y, 0*z+zl(1), '.')
rotate3d on
[X,Y,Z]=meshgrid(round(xl(1)):round(xl(2)),round(yl(1)):round(yl(2)),round(zl(1)):round(zl(2)));
V = X.^2+Y.^2+Z.^2;
contourslice(X,Y,Z,V,xl(2),yl(2),[zl(1) zl(2)])
hold off

MATLAB: Plot Solid Positive-Valued/Dashed Negative-Valued Contour Plot

The contour function itself cannot do that, however it is srtaightforward to adapt it:

[X,Y,Z] = peaks;
figure
hold on
[CM,cc] = contour(X,Y,Z,'ShowText','on');
cc.LineStyle = ':';
cc.Color = 'w';
Lvls = cc.LevelList;
PosIdx = find(ismember(CM(1,:),Lvls(Lvls>=0)));
PosLen = CM(2,PosIdx);
NegIdx = find(ismember(CM(1,:),Lvls(Lvls<0))); 
NegLen = CM(2,NegIdx);
for k = 1:numel(PosIdx)
    IdxRng = PosIdx(k)+1:PosIdx(k)+PosLen(k);
    plot(CM(1,IdxRng), CM(2,IdxRng), '-k')
end
for k = 1:numel(NegIdx)
    IdxRng = NegIdx(k)+1:NegIdx(k)+NegLen(k);
    plot(CM(1,IdxRng), CM(2,IdxRng), '--k')
end
hold off
axis('equal')

producing:

This overplots the original contours so that any text values remain visible (ini case you want them shown).

Best Answer

Related Solutions

MATLAB: Add contours to scatter3 plot

MATLAB: Plot Solid Positive-Valued/Dashed Negative-Valued Contour Plot

Related Question