I think i have problem with pause command

Hello dudes, i make a small animation on matlab about a body that start from Y=0 with initial velocity. My problem is that on the paper maths shows that the total time of the animation will be 4sec but when i run the programm does seem to be same running time. I think that my error is on the pause command but i can't solve it

tspan =0:0.01:4;
y0 = 0;
[t,y] = ode45(@(t,y) -10*t+20, tspan, y0);
plot(t,y)
grid on

x1=[0, 0, 1, 1];
y1=[0, 0.5, 0.5, 0];

x2=[0, 0, 10, 10];
y2=[0, 0.01, 0.01, 0];
fill(x2,y2,'black');
hold on
axis([0 10 -5 25])
grid on

time=0
z=1

while time<=400
    time=time+1;
    ypsos=y(z)
    p=fill(x1,y1+ypsos,[0 0.41 0.53])
    pause(0.009)
    drawnow
    delete(p);
    z=z+1;
    end

Answer 1

[Walter Roberson]

It is not obvious that you are filling the area that you would want to fill, but this at least finished quickly enough.

tspan =0:0.01:4;
y0 = 0;
[t,y] = ode45(@(t,y) -10*t+20, tspan, y0);
plot(t,y);
axis([0 10 -5 25])
grid on
hold on
drawnow();

x1=[0, 0, 1, 1];
y1=[0, 0.5, 0.5, 0];

x2=[0, 0, 10, 10];
y2=[0, 0.01, 0.01, 0];
fill(x2,y2,'black');
grid on

for time = 1 : 400
    ypsos=y(time);
    p=fill(x1,y1+ypsos,[0 0.41 0.53]);
    pause(0.009)
    drawnow
    delete(p);
end

[Walter Roberson]

If the idea is "real time" animation, then:

start = tic;
for time = 1 : 400
    ypsos=y(time);
    p=fill(x1,y1+ypsos,[0 0.41 0.53]);
    if time ~= 400
      pause(y(time+1) - toc(start));
    end
    delete(p);
end

Outputs will tend to be slightly late, but there should not be any cumulative drift as the time is compared to the start time rather than assuming that we started this round on time.

[Walter Roberson]

cla reset
tspan =0:0.01:4;
y0 = 0;
[t,y] = ode45(@(t,y) -10*t+20, tspan, y0);
plot(t,y)
grid on
x1=[0, 0, 1, 1];
y1=[0, 0.5, 0.5, 0];
x2=[0, 0, 10, 10];
y2=[0, 0.01, 0.01, 0];
fill(x2,y2,'black');
hold on
axis([0 10 -5 25])
grid on

start = tic;

p = fill(x1, y1, [0 0.41 0.53]);
for time = 1 : 400
ypsos=y(time);
p.YData = y1+ypsos;
pause(t(time+1)-toc(start));
end
toc(start)

Answer 2

[Luciano Garim]

Hi, sim ts.

To solve your problem, you may use the conditional command "if" and "return". Try to execute this code now.

tspan =0:0.01:4;
y0 = 0;
[t,y] = ode45(@(t,y) -10*t+20, tspan, y0);
plot(t,y)
grid on
x1=[0, 0, 1, 1];
y1=[0, 0.5, 0.5, 0];
x2=[0, 0, 10, 10];
y2=[0, 0.01, 0.01, 0];
fill(x2,y2,'black');
hold on
axis([0 10 -5 25])
grid on
time=0
z=1
while time<=1000
time=time+1;
if time>400
return;
end
ypsos=y(z)
p=fill(x1,y1+ypsos,[0 0.41 0.53])
pause(0.009)
drawnow
delete(p);
z=z+1;
end

I hope helped you!

[Walter Roberson]

return is not needed. If you want to stop at 400, just change the while limit. if / return approach here has nothing to recommend it over the approach the original person used.

Answer 3

[sim ts]

I think that on this simple problem it is a litte bit irelevant what kind of loop you will use. My problem is that i want the body to start from Y0=0 --->t0=0 second and to stop again at Yf=0--->tf=4 second but when i measue the time it doesn't corresponding on my result and i try to get smaller pause like pause(0.001) and t doesn't change.

[Walter Roberson]

pause() has no effect on the calculation other than to delay it.

pause() has an effect on the plotting, in that it has the side effect of triggering immediate drawing.

WIth the code I posted, you get an animation of a bar floating upwards and back downwards.

when i measue the time it doesn't corresponding on my result

How are you measuring time?

Are you trying to animate in "real time", something displaying in the screen at elapsed time according to t(time) ?

[sim ts]

I use Run and Time to measure the duration of the animation. If you see the ode45 plot on x axis is the time and on y is the altitude so by seeing the plot you guess that the object start to moving upwords at t=0 and the maximun altitude is y=20 at t=2 second and the simulation ands when the object reach y=0 at t=4. My problem is that on the animation i can't have the same time and i get bigger.

[sim ts]

also to measure the time i use tic toc commands

tic
while time<=400
time=time+1;
ypsos=y(z)
p=fill(x1,y1+ypsos,[0 0.41 0.53])
pause(0.01)
drawnow
delete(p);
z=z+1;
end
toc