plotyy : align y axes at zero

When using plotyy I need to plot two different series. One on the left y axis, and the other on the right y axis. Both series contain numbers in different scales. The one of the left contains numbers from 0 to (potentially) Infinity, but the one on the right is restricted to the range -1, 1. In the code below, you can see an example.

I'd like to make sure that both axes cross at y = 0, but I'm not sure how to do it. In the example I included, you can see that the two y axes are misaligned.

Thanks in advance

x = 15; 
fn1 = @(x, y) bar(x, y, 0.3, 'FaceColor', 'blue');
fn2 = @(x, y) bar(x, y, 0.3, 'FaceColor', 'red'); 
figure; 
plotyy( [1:x]-1, rand(x, 1) * 100, [1:x]+1, 2 * rand(x, 1) - 1, fn1, fn2)

Answer 1

[Oleg Komarov]

A quick fix, call plotyy as:

ax = plotyy(...)

Then set limits of axes

set(ax(1),'Ylim',max(get(ax(1),'Ylim')) * [-1 1])

EDIT General solution with ratio of negative leg over positive

% Retrieve Ylim of second axis
ylim2 = get(ax(2),'Ylim');
% Ratio of negative leg to positive one (keep sign)
ratio = ylim2(1)/ylim2(2);
% Set same ratio for first axis
ylim1 = get(ax(1),'Ylim');
set(ax(1),'Ylim',[ylim1(2)*ratio ylim1(2)])

[Mark]

First of all, thanks for taking the time to read and answer my question.

The example I put was simply for simplification purposes. Although the range of the secondary axes is [-1, 1], the numbers I plot may not cover all that range. For instance, in the example I used, the second series with the following:

[ax, ~, ~] = plotyy( [1:x]-1, rand(x, 1) * 100, [1:x]+1, (-0.2:(0.8--0.2)/(x-1):0.8), fn1, fn2)

Then use your fix and you will see that it doesn't solve the problem. if you set the limits of the secondary axes to [-1, 1]:

set(ax(2),'Ylim',[-1 1])

Then the axes are aligned at zero but there is a huge amount of space between y=0, and y=-1

I was looking for a more general solution. In my particular case, the negative values are rare but when they happen they are usually closer to 0 than to -1. Conversely, the positive values can be up to zero, but they usually are less than 0.9.