Matlab axes scaling

Question

how exactly do you get fixed scaling of axes in Matlab plot when plotting inside a loop? My aim is to see how data is evolving inside the loop. I tried using axis manual and axis(...) with no luck. Any suggestions?

I know hold on does the trick, but I don't want to see the old data.

Solution 1

If you want to see your new plotted data replace the old plotted data, but maintain the same axes limits, you can update the x and y values of the plotted data using the SET command within your loop. Here's a simple example:

hAxes = axes;                     %# Create a set of axes
hData = plot(hAxes,nan,nan,'*');  %# Initialize a plot object (NaN values will
                                  %#   keep it from being displayed for now)
axis(hAxes,[0 2 0 4]);            %# Fix your axes limits, with x going from 0
                                  %#   to 2 and y going from 0 to 4
for iLoop = 1:200                 %# Loop 100 times
  set(hData,'XData',2*rand,...    %# Set the XData and YData of your plot object
            'YData',4*rand);      %#   to random values in the axes range
  drawnow                         %# Force the graphics to update
end

When you run the above, you will see an asterisk jump around in the axes for a couple of seconds, but the axes limits will stay fixed. You don't have to use the HOLD command because you are just updating an existing plot object, not adding a new one. Even if the new data extends beyond the axes limits, the limits will not change.

Solution 2

You have to set the axes limits; ideally you do that before starting the loop.

This won't work

x=1:10;y=ones(size(x)); %# create some data
figure,hold on,ah=gca; %# make figure, set hold state to on
for i=1:5,
   %# use plot with axis handle 
   %# so that it always plots into the right figure
   plot(ah,x+i,y*i); 
end

This will work

x=1:10;y=ones(size(x)); %# create some data
figure,hold on,ah=gca; %# make figure, set hold state to on
xlim([0,10]),ylim([0,6]) %# set the limits before you start plotting
for i=1:5,
   %# use plot with axis handle 
   %# so that it always plots into the right figure
   plot(ah,x+i,y*i); 
end

Comments

[Amro]

+1 I also have a couple of suggestions: 1) to avoid flickering, you should enable double buffering set(gcf,'DoubleBuffer','on'). 2) if you want to increase the speed of drawing and get a smoother animation, set the EraseMode property to something other than 'normal' (I would use xor in this case). Of course you'll have to use low-level functions like line,patch,text,etc.. Check out this guide for more details: mathworks.com/support/tech-notes/1200/1204.html#Section%2023