How can I show this shape moving along the trajectory?

This only generates the projectile at the end of the trajectory. The shape should start at (0,20) and end at (20,100)and scale from 100% to 25%

function v = problem1

% coordinates of square under one variable square = [0, 4, 4, 0;0, 0, 4, 4];

% generate animation window figure

xmin = -5;

xmax = 25;

ymin = -5;

ymax = 125;

axis equal

axis([xmin xmax ymin ymax])

hold on

%setting your trajectory

t = linspace(0,20,500); % independent variable of your function

trajectory = 1/4*t.^2; % represents y in y = t^2

scale = .99;

    for i = 500
% object moving along projectile
    h = fill(square(1,:) + t(i),square(2,:) + trajectory(i),'r');
    hold on;
% scales the figure from 100% to 25%
        fill(scale*square(1,:) + t(i), scale*square(2,:) + trajectory(i), 'r');
    hold on;
         % do not change below 2 lines, should follow your fill command
         v.x(i,:)=get(h,'xdata')';
         v.y(i,:)=get(h,'ydata')';
    pause(.3)

    end

end

[Jan]

Please describe the problems you have with the shown code.

What does "scales the figure from 100% to 25%" mean?

Answer 1

[Eugene]

1. your for loop definition should be

i=1:500

2. you didn't have an algorithm to change the value of scale.

3. scale will not work to shrink the size of the square (i'm assuming that is what you're tyring to do) because the original coordinates do not put the centroid of the square at zero.

Try this:

square = [-2, 2, 2, -2;-2, -2, 2, 2];
figure;

xmin = -5;
xmax = 25;
ymin = -5;
ymax = 125;
axis equal
axis([xmin xmax ymin ymax])
hold on

N = 50;
t = linspace(0,20,N); 
trajectory = 1/4*t.^2;
scale = linspace(1,0.25,N);
for i = 1:N
    % object moving along projectile
    h = fill(square(1,:) + t(i),square(2,:) + trajectory(i),'r');
    hold on;
    % scales the figure from 100% to 25%
    fill(scale(i)*square(1,:) + t(i), scale(i)*square(2,:) + trajectory(i), 'r');
    hold on;
    pause(0.3)
end

Otherwise if you don't want to have a persistent image then just change the x and y data for the filled object.

square = [-2, 2, 2, -2;-2, -2, 2, 2];
figure;

xmin = -5;
xmax = 25;
ymin = -5;
ymax = 125;
axis equal
axis([xmin xmax ymin ymax])
hold on

N = 50;
t = linspace(0,20,N); 
trajectory = 1/4*t.^2;
scale = linspace(1,0.25,N);
h1 = fill(square(1,:) + t(1),square(2,:) + trajectory(1),'r');
h2 = fill(scale(1)*square(1,:) + t(1), scale(1)*square(2,:) + trajectory(1), 'r');
for i = 2:N
    % object moving along projectile
    set(h1,'XData',square(1,:) + t(i),'YData',square(2,:) + trajectory(i));
    hold on;
    % scales the figure from 100% to 25%
    set(h2,'XData',scale(i)*square(1,:) + t(i),'YData',scale(i)*square(2,:) + trajectory(i));
    hold on;
    pause(0.3)
end