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on 10 Oct 2021

% Remix of Jr's "Hourglass"

% Create hourglass profile

d=-2:.01:1.2;

p=1./(1+exp(2*d)); % 1/2 the hourglass profile (sigmoidal)

r=[p,flip(p)]; % radii

% Convert profile to surface

t=(0:.01:6.3)';

z=linspace(0,4,642).*(t*0+1); % constants are numel(r) and numel(t)

% Plot hourglass

axes(Colorm=gray,vis=0,vie=[0,9])

hold

Current plot held

surf(r.*cos(t),r.*sin(t),z,EdgeC='n',FaceA=.2)

light

axis equal

% add grains

v=[400,160];

d=(rand(v)-.5).*p(1:2:320)*1.8; %radial distance from XY origin

a=rand(v)*7; % angular position (radians)

plot3(d.*cos(a),d.*sin(a),z(1,10:169),'.')