How to change the Ytick in the secondary y axis?

I have a figure with the following code. How can I add 20 and 80 to the secondary y label? Now it looks like this:

axes1 = axes('Parent',figure(15),'YTick',[8.5 9.5 10.5],'Color',[0 0 0]);
[ax,p1,p2] = plotyy(annual(:,1),annual(:,7),lc2(:,1),lc2(:,2:3));
hold on
set(p1,'LineStyle',':','Marker','v','DisplayName','DO')
set(p2(1),'LineStyle','--','Marker','*','Color',[1 0 0],'DisplayName','Developed')
set(p2(2),'LineStyle','--','Marker','*','Color',[0 0.5 0],'DisplayName','Forest')

[p,~,mu] = polyfit(annual(8:20,1),annual(8:20,7),3)
f = polyval(p,annual(8:20,1),[],mu);
hold on
plot(annual(8:20,1),f,'k','DisplayName','DO Trendline')

xlabel('Time')
ylabel(ax(1),'DO (mg/l)') % left y-axis
ylabel(ax(2),'Area (%)') % right y-axis
ylim(ax(1), [8.5 10.5]);
ylim(ax(2), [0 100]);
legend(axes1,'show');

Answer 1

[Star Strider]

I can’t reproduce your plot because I don’t have your data, but this code snippet offers a workable approach:

x = [1992:2012];
y1 = randi([10 35], 1, length(x));
y2 = randi([65 80], 1, length(x));

figure(1)
[ax,p1,p2] = plotyy(x,y1, x,y2);
ylim(ax(2), [0 100]);
set(ax(2), 'YTick',[0, 20, 50, 80, 100])

The last line sets the ticks where you want them and labels them.