How to get the values of the XAxis Minor Ticks (of an inset plot)

I have an inset plot, in a log-scale, and I would like to get the values of its XAxis Minor Ticks, with the following command:

ax2.XAxis.MinorTickValues

However, when I run the following code

% create a plot
x1 = linspace(0,1000);
y1 = sin(2*pi*x1);
plot(x1,y1)
set(gca,'Fontsize',20,'FontWeight','normal','LineWidth',1);

% create the inset plot
ax2 = axes('Position',[.45 .45 .4 .4]);
box on
plot(x1,y1)              % <-- inset plot
set(ax2,'XScale','log')  % <-- set log-scale for the x-axis of the inset plot
set(ax2,'Fontsize',20,'FontWeight','normal','LineWidth',1);

% Result
ax2.XAxis.MinorTickValues

ans =

     []

In other words, the followin command

ax2.XAxis.MinorTickValues

returns an empty array!

Another comment: if I go to the Command Window (when the figure is still on the monitor of the computer) and I type the same command, I get the correct values

>> ax2.XAxis.MinorTickValues

ans =

  Columns 1 through 9

          10          20          30          40          50          60          70          80          90

  Columns 10 through 18

         100         200         300         400         500         600         700         800         900

  Column 19

        1000
        
        

How can I get the values of the XAxis Minor Ticks of an inset plot, within a code, and not as an "external command", in the Command Window?

Answer 1

[Gayathri]

Hello @Sim,

I understand that you are getting an empty array while running "ax2.XAxis.MinorTickValues" in code but getting output while running the same code in command window. It might be due to the timing of when the "MinorTickValues" property is being accessed. In MATLAB, certain properties, like "MinorTickValues", may not be initialized until the plot is fully rendered and visible. You can use "drawnow" to force MATLAB to complete the rendering of the figure before accessing the "MinorTickValues" property as shown below.

drawnow;
ax2.XAxis.MinorTickValues

For more information about "drawnow" you can refer the below mentioned link.

https://www.mathworks.com/help/matlab/ref/drawnow.html

Hope this resolves the issue mentioned.

[Sim]

Thanks a lot @Gayathri :-)

Answer 2

[Star Strider]

Assign the output to a variable —

% create a plot
x1 = linspace(0,1000);
y1 = sin(2*pi*x1);
plot(x1,y1)
set(gca,'Fontsize',20,'FontWeight','normal','LineWidth',1);

% create the inset plot
ax2 = axes('Position',[.45 .45 .4 .4]);
box on
plot(x1,y1)              % <-- inset plot
set(ax2,'XScale','log')  % <-- set log-scale for the x-axis of the inset plot
set(ax2,'Fontsize',20,'FontWeight','normal','LineWidth',1);

% Result
ax2.XAxis.MinorTick = true

ax2 = 
  Axes with properties:

             XLim: [10 1000]
             YLim: [-1 1]
           XScale: 'log'
           YScale: 'linear'
    GridLineStyle: '-'
         Position: [0.4500 0.4500 0.4000 0.4000]
            Units: 'normalized'

  Use GET to show all properties

ax2_mtv = ax2.XAxis.MinorTickValues

ax2_mtv = 1x19

10 20 30 40 50 60 70 80 90 100 200 300 400 500 600 700 800 900 1000

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For some reason, this is being inconsistent here. It appears to be necessary first to turn the minor ticks on, and second not to suppress (with at trailing semicolon ‘;’) the command that turns them on. I get the same behaviour in MATLAB Online. This behaviour may be a bug.

EDIT — Corrected typographical errors.

.

[Sim]

Thanks a lot @Star Strider :-)

I tried your solution by adding the axes limits, and it looks like that solution does not work anymore... :-(

% create a plot
x1 = linspace(0,1000);
y1 = sin(2*pi*x1);
plot(x1,y1)
set(gca,'Fontsize',20,'FontWeight','normal','LineWidth',1);

% create the inset plot
ax2 = axes('Position',[.45 .45 .4 .4]);
box on
plot(x1,y1)              % <-- inset plot
set(ax2,'XScale','log')  % <-- set log-scale for the x-axis of the inset plot
set(ax2,'Fontsize',20,'FontWeight','normal','LineWidth',1);

% Set the axes limits
xlim([0 60])
ylim([0 Inf])

% Result
ax2.XAxis.MinorTick = true

ax2 = 
  Axes with properties:

             XLim: [0 60]
             YLim: [0 Inf]
           XScale: 'log'
           YScale: 'linear'
    GridLineStyle: '-'
         Position: [0.4500 0.4500 0.4000 0.4000]
            Units: 'normalized'

  Use GET to show all properties

ax2_mtv = ax2.XAxis.MinorTickValues

ax2_mtv =

     []

[Sim]

Instead, if I use the @Gayathri solution, it works also when setting the axes limits.....

% create a plot
x1 = linspace(0,1000);
y1 = sin(2*pi*x1);
plot(x1,y1)
set(gca,'Fontsize',20,'FontWeight','normal','LineWidth',1);

% create the inset plot
ax2 = axes('Position',[.45 .45 .4 .4]);
box on
plot(x1,y1)              % <-- inset plot
set(ax2,'XScale','log')  % <-- set log-scale for the x-axis of the inset plot
set(ax2,'Fontsize',20,'FontWeight','normal','LineWidth',1);

% Set the axes limits
xlim([0 60])
ylim([0 Inf])

% Result
drawnow
ax2_mtv = ax2.XAxis.MinorTickValues

ax2_mtv = 1x7

15 25 30 35 45 50 55

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[Star Strider]

My pleasure!

I have no idea what the problem is. The solutiion I posted worked for me here and in MATLAB Online.

It works if I re-position the call to it —

% create a plot
x1 = linspace(0,1000);
y1 = sin(2*pi*x1);
plot(x1,y1)
set(gca,'Fontsize',20,'FontWeight','normal','LineWidth',1);

% create the inset plot
ax2 = axes('Position',[.45 .45 .4 .4]);
box on
plot(x1,y1)              % <-- inset plot
set(ax2,'XScale','log')  % <-- set log-scale for the x-axis of the inset plot
set(ax2,'Fontsize',20,'FontWeight','normal','LineWidth',1);

ax2.XAxis.MinorTick = true

ax2 = 
  Axes with properties:

             XLim: [10 1000]
             YLim: [-1 1]
           XScale: 'log'
           YScale: 'linear'
    GridLineStyle: '-'
         Position: [0.4500 0.4500 0.4000 0.4000]
            Units: 'normalized'

  Use GET to show all properties

ax2_mtv = ax2.XAxis.MinorTickValues

ax2_mtv = 1x19

10 20 30 40 50 60 70 80 90 100 200 300 400 500 600 700 800 900 1000

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% Set the axes limits
xlim([0 60])
ylim([0 Inf])

% Result
% % ax2.XAxis.MinorTick = true
% ax2_mtv = ax2.XAxis.MinorTickValues

This behaviour is just strange!

.

[Sim]

Yes, it is very strange... and I do not understand the reasons behind this behaviour...

[dpb]

"... and I do not understand the reasons behind this behaviour..."

Buried in the innards of HG2; it attempts to minimize the number of screen refreshes to keep graphics response time as quick as possible.

I would hypothesize that the requested action of simply returning the values doesn't trigger a screen refresh because nothing has happened that will cause the graphics display to change so there is no need for a refresh at that point programmatically. Changing the focus to the command window, otoh, causes a refresh and then the internal data have been updated.

I tried the same thing as @Star Strider and got it to work the first time, but then it didn't later; only Mathworks would have the ability to actually explain explicitly why...

[Sim]

Thanks @dpb :-)

Answer 3

[dpb]

@Gayathri recognized the underlying problem which can be very confusing because it is so erratic in what does/does not get updated there's no predicting what operation(s) require it -- and it's rare enough it is almost never on one's radar unless one just happens to "get bit" a second time recently enough after having had a first occurrence.

However, for complicated handling of such graphics, I would strongly recommend keeping a better track of object handles; my first thought was that since the code wasn't encapsulated in a function the axes handles were getting mixed up and you were accessing another axis in the command window, but that alone didn't always solve the problem; it worked once and like @Star Strider's thoughts, thought had it solved, but then a second run after adding only some additional comments, not code, it failed again and couldn't get it to work correctly even reverting back. It's truly a mind-boggling symptom when it does occur.

Anyways, I'd suggest something more on the order of

% create a plot
x1 = linspace(0,1000);
y1 = sin(2*pi*x1);
hF=figure;                                                          % create a figure handle to put stuff into...
hAx1=axes(hF,'Fontsize',20,'FontWeight','normal','LineWidth',1);    % put the axes in the desired figure
hL1=plot(hAx1,x1,y1);                                               % and the first line in that axis

% create the inset plot
hAx2=axes(hF,'Position',[.45 .45 .4 .4],'Fontsize',20,'FontWeight','normal','LineWidth',1, ...
              'box', 'on');

hL2=plot(hAx2,x1,y1);              % <-- inset plot
hAx2.XScale='log';

drawnow
hAx2.XAxis.MinorTickValues

ans = 1x19

10 20 30 40 50 60 70 80 90 100 200 300 400 500 600 700 800 900 1000

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Now you have access to everything specifically and are sure are talking to the right object and focus is where intend it to be...

[Sim]

@dpb thanks a lot :-) ....so, basically, the idea is to "refine" the @Gayathri solution?!

[dpb]

Yes; he/she(?) identified the root cause so simply adding drawnow fixes your original code; all I did was ensure that that code actually addresses the specific axes intended and isn't then subject to an inadvertent change of focus since without an explicit parent object handle the target will always be whatever gca() returns and that can change if something else happens. Plus, simply having all the handles available lets you do anything else you want to do later on without having to try to go "handle diving" to retrieve them.

[Sim]

Ah ok, clear, thanks for the explaation! So, again, I do not know which answer to accept here since they are all nice...at least I upvote all the answers :-) Maybe someone can give an hint on which answer is the most appropriate here :-)

[dpb]

Well, that depends... :) I agree @Gayathri was the first to identify the issue w/ the event queue not being updated and that drawnow solves the initial issue, so precedence goes there. Personally, whether or not I was the one to point it out and provide the other code, in cases of mixing multiple axes I think good practice is to always identify the actual objects...

[Sim]

Yes, sorry, I need to give credit to @Gayathri for identifying the issue first. I am using your sligtly more sophisticated solution, even though the initial hint comes from @Gayathri........ I would really like to accept all the answers... I could, mabye, accept the @Gayathri answer, and ask if people could upvote your answer in order to reach 4 points each, or, viceversa... You all deserve credit!

Also the @Star Strider solution is cool :-)