How can I compare the scale of two y axis in a subplot and adjust them to each other?

Hello MatLab-Pros,

I have the following code:

hAxes(1) = subplot(4,1,1);

          yyaxis left
          plot(x, y1)
          ScaleR = get(gca, 'YTickLabel');

          yyaxis right
          plot(x, y2)

          if strncmp(fname1, fname2, 5) == 1
              set(gca, 'YTickLabel', ScaleR)
          end

I should change the scale of the right axis to the scale of the left axis if fname1 and fname2 are the same (which they are for sure), but it doesnt do anything. Where am I wrong here? And is it possible to do this both-ways? Meaning, matlab should compare the two ranges of the axis and set the larger one for both sides.

Thanks in advance.

Mike

EDIT: With the changes that "Walter Roberson" suggested my code looks like this:

hAxes(1) = subplot(4,1,1);

          yyaxis left
          yaxL = gca;
          plot(yaxL, x, y1);

          yyaxis right
          yaxR = gca;
          plot(yaxR, x, y2)

          if strncmp(fname1, fname2, 5) == 1
               YLL = yaxL.YLim;
               YLR = yaxR.YLim;
               YLC = [min(YLL(1), YLR(1)), max(YLL(2), YLR(2))];
               yaxL.YLim = YLC;
               yaxR.YLim = YLC;
               yaxR.YTick = yaxL.YTick;
          end

The Problem is the output looks like this: (First graph is with the selfmade adjustments to the scale, second one is default matlab scaling)

[Michael Steinbuechler]

BTW: If I use the get command the values for YLL and YLR are both [1.5000 2.5000]

[Adam]

Don't use gca, always refer to specific axes handles. You have two axes in a plot such as the above. Just relying on gca to give you the right one is very hit and miss!

[Michael Steinbuechler]

Where can I assign handles to the different axis? yyaxis has no output and on plot I get the error: There is no YLim property on the Line class.

[Jan]

Please post your code such that we can suggest an improvement.

Answer 1

[Walter Roberson]

get(gca, 'YLim')

for each of the two axes, recording the values. Take min of the first component and max of the second component; set the YLim to the result for both axes.

[Michael Steinbuechler]

Unfortunatly it still doesnt work. Here is my plot:

The upper graph is with the code for the axis scaling and the second one is just default matlab scaling. It's the same

[Michael Steinbuechler]

If I use the get command on the right axis, it gives me the correct limits, but it seems, that the graph doesnt get updated

[Walter Roberson]

          hAxes(1) = subplot(4,1,1);

          yyaxis left
          yaxL = gca;
          plot(yaxL, x, y1)

          yyaxis right
          yaxR = gca;
          plot(yaxR, x, y2)

          if strncmp(fname1, fname2, 5) == 1
             YLL = yaxL.YLim;
             YLR = yaxR.YLim;
             YLC = [min(YLL(1), YLR(1)), max(YLL(2), YLR(2))];
             yaxL.YLim = YLC;
             yaxR.YLim = YLC;
             yaxR.YTick = YaxlL.YTick;
          end

[Michael Steinbuechler]

Very smooth solution, but my output doesnt seem to agree:

[Walter Roberson]

Sorry I need to sleep now. You could compare yaxL.YTick and yaxR.YTick and also YTickLabel properties

[Michael Steinbuechler]

Okay, thanks so far

[Adam]

Yeah, yyaxis does do some odd things. It is actually only one axis so the approach above to get an explicit axes handle does not work because

yyaxis right

changes the one axes to have its y axis location on the right so both stored axes handles are the same one.

What you need to get hold of is:

YLL = hAxes(1).YAxis(1).Limits

and

YLR = hAxes(1).YAxis(2).Limits

and then proceed as per Walter's answer.

[Michael Steinbuechler]

I did this, but things are getting wierd now. Thats my new output:

If I check the variables I get this numbers:

YLL [1.8000 2.4000] YLR [1.5000 2.5000] YLC [1.5000 2.5000]

It seems the command to assign the new range to the axis does not work (but I dont get an error or anything)

hAxes(1) = subplot(4,1,1);

          yyaxis left
          plot(x, y1)

          yyaxis right
          plot(x, y2)

          if strncmp(fname1, fname2, 5) == 1

             YLL = hAxes(1).YAxis(1).Limits;
             YLR = hAxes(1).YAxis(2).Limits; 
             YLC = [min(YLL(1), YLR(1)), max(YLL(2), YLR(2))];

             hAxes(1).YAxis(1).Limits = YLC;
             hAxes(1).YAxis(2).Limits = YLC;

          end

[Michael Steinbuechler]

Okay I finally found a way that works as well. I can find the minimum and maximum value from y1 and y2 with the "min" and "max" commands and than just do it this way:

yyaxis left
        plot(tData, x1a)
        ylim([min1 max1])

          yyaxis right
          plot(tData, x1b)
          ylim([min1 max1])

Answer 2

[Jan]

Perhaps this helps: https://www.mathworks.com/help/matlab/creating_plots/customize-graph-with-two-y-axes.html

[Michael Steinbuechler]

I already saw this and it doesnt really help. Acoording to this site, it should work how I did it.