Pause(n) vs timer. Which is better?

22 次查看（过去 30 天）
Caleb
Caleb 2013-7-26
So I'm trying to show a plot of time dependent data as if it is taken in real time. The issue with using the pause(n) function within a for-loop is that the loop performance deteriorates, and plotting the functions drastically slows down. Can this be remedied with a timer? And how could I achieve the same outcome as the code below using a timer?
Here's the code:
% inputs
t = 1:0.05:25;
% time-dependent functions
sin_t = sin(t);
cos_t = cos(t);
% loop for time-dependent measurements
n = numel(t)
figure, xlim([min(t) max(t)]), ylim([-2 2]);
hold on
for i = 1:n
plot (t(1:i), sin_t(1:i));
plot (t(1:i), cos_t(1:i));
pause(0.01);
end
hold off
  2 个评论
kjetil87
kjetil87 2013-7-26
编辑：kjetil87 2013-7-26
you could offcourse use timers, but you could also gain something on not replotting the same data.
you could for instance try with:
for i=1:n-1
plot( t(1+i-1:i+1) , sin_t(1+i-1:i+1) )
...
then you wont use unnecessary time plotting stuff that is already in your plot.
Sean de Wolski
Sean de Wolski 2013-7-26
@kjetil: an even bigger improvement is to not call PLOT again. Calling plot requires creating an additional line which has its own overhead. It's more efficient to change the data of the existing line object like I did below. NOTE, you could do this in a for-loop as well as in the timer callback.

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Sean de Wolski
Sean de Wolski 2013-7-26
I always recommend using timers. They require a little bit more effort to become familar with but are much more powerful. They also emulate a multithreaded environment so you can continue to use the command line while they are running. Here is your example with a timer.
function timerEx
% inputs
t = 1:0.05:25;
% time-dependent functions
sin_t = sin(t);
cos_t = cos(t);
% loop for time-dependent measurements
n = numel(t);
figure, xlim([min(t) max(t)]), ylim([-2 2]);
hold on
%Plot first point, store handles so we can update the data later.
h(1) = plot (t(1), sin_t(1));
h(2) = plot (t(1), cos_t(1));
%Build timer
T = timer('Period',0.01,... %period
'ExecutionMode','fixedRate',... %{singleShot,fixedRate,fixedSpacing,fixedDelay}
'BusyMode','drop',... %{drop, error, queue}
'TasksToExecute',n-1,...
'StartDelay',0,...
'TimerFcn',@tcb,...
'StartFcn',[],...
'StopFcn',[],...
'ErrorFcn',[]);
% Start it
start(T);
%Nested function! Has access to variables in above workspace
function tcb(src,evt)
%What task are we on? Use this instead of for-loop variable ii
taskEx = get(src,'TasksExecuted');
%Update the x and y data.
set(h(1),'XData',t(1:taskEx),'YData',sin_t(1:taskEx));
set(h(2),'XData',t(1:taskEx),'YData',cos_t(1:taskEx));
drawnow; %force event queue flush
end
end
  9 个评论
显示 7更早的评论
Sean de Wolski
Sean de Wolski 2013-7-29
@Daniel, Why not?
You could use the wait() method of the timer to force it to wait.
Daniel Shub
Daniel Shub 2013-7-29
I like a loop better than a timer for two reasons. First, the error handling of callbacks is really bad in that an error in a callback doesn't stop the main thread. Second, timer callbacks can interrupt between any two "commands", even if those commands need to occur close together in time or leave an object in an unstable state. With a 10ms period and a callback that operates on graphic objects, it doesn't seem like there will be enough time for a second thread to be useful.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Code Execution 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by