Computer Science  MATLAB
posted by Lee on .
Thanks MathMate. Print plotting sounds awful O_O. What you suggested was correct and this code worked
disp('Problem 13.9')
x=[2*pi:.00001*pi:2*pi];
a=0;
y=sin(xa);
g=plot(x,y);
title(sprintf('sin(x%.2f)\n',a))
grid on;
set(g,'EraseMode','xor')
while a<=8*pi
a=a+.1*pi;
y=sin(xa);
plot(x,y)
title(fprintf('sin(x%.2f)\n',a))
grid on;
drawnow
end
I have another question though that I seem to be struggling with.
Create an animation of the following:
Let x vary form 2pi to +2pi
Let y=sin(x)
Let z=sin(xa)cos(ya)
Let a be the animation variable.
Remember that you'll need to mesh x and y to create twodimensional matrices; use the resulting arrays to find z.
Here's my attempt at a solution.
x=2*pi:pi/50:2*pi;
y=sin(x);
[X,Y]=meshgrid(x,y);
z=sin(X)*cos(Y);
h=surf(z);
axis tight
set(gca,'nextplot','replacechildren');
shading interp
colormap(jet)
for a=0:pi/100:8*pi
z=sin(Xa)*cos(Ya);
set(h,'zdata',z);
drawnow
end
When I try to run it the axes are colored for like a tenth of a second and then it just turns to white. I don't know exactly what I'm doing wrong.

I had a quick look at the code, and I suggest the following changes (just a guess).
I believe the code has worked as expected, but the duration of the animation is only about 1/10th of a second.
To test the hypothesis, change
for a=0:pi/100:8*pi
to
for a=0:pi/1000:8*pi
to make 10 times more frames. If it stays for about a second, then it is the problem.
The other "problem" that it stays white at the end is probably the endpoint (8π) puts everything to zero, so it is/may be coloured white.
Try changing the endpoint to, say
8.5π or 8.25π and see if it makes a difference.
Let me know how it goes. 
I tried both and both results leave me with the same result, It just flashes real quick and then turns white... I even tried a=0:pi/1000000000:8*pi, it stays for a little bit longer but then turns white....
I think it's an issue with something else... what I'm not exactly sure as it's strange that something does appear but then quickly disappears... 
A couple of things you could try:
1. put
refreshdata
before "drawnow".
Hopefully this will update every frame of the image.
2. put a finer grid, such as
x=2*pi:pi/500:2*pi;
instead of 50.
Sorry that I cannot be more definite because I don't have access to Matlab, especially the plotting part. 
Same thing. I wounder if I'm suppose to be using the surfz function and not some other 3 dimensional plotting function?

got it
<_< forgot the dot and got rid of the axis tight
disp('Problem 13.11')
x=2*pi:pi/50:2*pi;
y=sin(x);
[X,Y]=meshgrid(x,y);
z=sin(X)*cos(Y);
h=surf(z);
set(gca,'nextplot','replacechildren');
shading interp
colormap(jet)
for a=0:pi/100:8.25*pi
z=sin(Xa).*cos(Ya);
set(h,'zdata',z);
drawnow
end 
Great! I missed that too (the dot).