In 2012, I researched computational materials science/physics for Dr. Dimitrios Papaconstantopoulos. The following is my semester report. All source code is listed at the end of the report.

# Category: Matlab

## Matlab: Smooth Rotating Animation for Line Plots

I recently became stuck trying to create an animation which consists of a smooth rotation of a viewpoint around the Lorenz attractor. Methods I use for changing viewpoints with respect to surface objects were creating jerky, lagging animations when applied to my line plot.

This will work for any 3D line plot.

plot3(x,y,z); axis vis3d fps = 60; sec = 10; vidObj = VideoWriter('plotrotation.avi'); vidObj.Quality = 100; vidObj.FrameRate = fps; open(vidObj); for i=1:fps*sec camorbit(0.9,-0.1); writeVideo(vidObj,getframe(gcf)); end close(vidObj);

## Matlab: Coaxial Cylinders (Polar Coordinates)

Let’s say we want to create an aesthetically pleasing visualization of 2 coaxial cylinders.

To do this, we’ll be adjusting the lighting, proportions, and transparency of the figure.

The code to create this figure utilizes the coordinate transformation from Cartesian to 3D-Polar coordinates. Recall that the transformation between coordinate systems is as follows.

*Side note:*

*I used phi above in the transformation equations and theta below in the code to make a point. The angular coordinate in the cylindrical (a.k.a polar) coordinate system is generally represented as either phi or theta.*

*These are equivalent, and the variable chosen is purely a matter of notation.*

Y=-5:5; theta=linspace(0,2*pi,40); [Y,theta]=meshgrid(Y,theta); r = 1.5 % calculate x and z X=r*cos(theta); Z=r*sin(theta); hs = surf(X,Y,Z) set(hs,'EdgeColor','None', ... 'FaceColor', [0.5 0.5 0.5], 'FaceLighting', 'phong'); alpha(0.7); hold on camlight right; r = 0.5 % recalculate x and z X=r*cos(theta); Z=r*sin(theta); hs = surf(X,Y,Z) axis equal set(hs,'EdgeColor','None', ... 'FaceColor', [0.5 0.5 0.5], 'FaceLighting', 'phong'); alpha(0.7); axis off camlight right; lighting gouraud view(140, 24) % white background set(gcf,'color','white')

## Matlab: Lorenz Attractor

I’m a big fan of the Lorenz Attractor, which, when plotted, resembles the half open wings of a butterfly. This attractor was derived from a simplified model of convection in the earth’s atmosphere. One simple version of the Lorenz attractor is pictured below:

The Lorentz system is a set of ordinary differential equations notable for its chaotic solutions (see below). Here $x$, $y$ and $z$ make up the system state,** **$t$ is time, and $sigma, row, beta$ are the system parameters.

The Lorentz attractor is a chaotic solution to this system found when $row = 28, sigma = 10. beta = 8/3$.

The series does not form limit cycles nor does it ever reach a steady state.

We can calculate and render the aforementioned chaotic solution to this ODE as follows:

function loren3 clear;clf global A B R A = 10; B = 8/3; R = 28; u0 = 100*(rand(3,1) - 0.5); [t,u] = ode45(@lor2,[0,100],u0); N = find(t>10); v = u(N,:); x = v(:,1); y = v(:,2); z = v(:,3); plot3(x,y,z); view(158, 14) function uprime = lor2(t,u) global A B R uprime = zeros(3,1); uprime(1) = -A*u(1) + A*u(2); uprime(2) = R*u(1) - u(2) - u(1)*u(3); uprime(3) = -B*u(3) + u(1)*u(2);

This results in the figure:

## Matlab: Create Mesh or Surface From Line Plot

This is a continuation of Matlab: Lorentz Attractor, however, these methods can be applied to any line plot or collection of points.

A slightly more aesthetically pleasing representation of the Lorentz Attractor can be achieved by adding axis off. And altering the view’s azimuth and elevation: view(15, 48).

tri = delaunay(x,y); plot(x,y,'.') %determine amount of triangles [r,c] = size(tri); disp(r) %plot with trisurf h = trimesh(tri, x, y, z, 'FaceAlpha', 0.6); alpha = 0.4 view(15, 48) axis vis3d axis off l = light('Position',[-50 -15 29]) lighting phong shading interp