Wrong axis value in correlation plot

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JT Yang 2019-7-13

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编辑： Amin Salehi 2023-12-7

Hi, I used correlation plot(corrplot) and getting the following graph. And it is obvious the var2 is bounded by -1 from the two scatter plot and as well as from the data. But the second histogram starts from a starting value much smaller value. I'm not sure is it a bug or my setting problem. Actually I did not do any settings, this is the default output from corrplot.

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the cyclist 2019-7-13

Can you upload your data and code? This would make your problem easier to diagnose.

JT Yang 2019-7-13

matlab.mat

Hi, it is simple two columns of data as in the attachment.

command used:

load('matlab.mat')

corrplot(MCMC)

MATLAB R2019A linux version

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Answer 1

the cyclist 2019-7-13

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I don't have the Econometrics Toolbox, so I can't confirm myself. But if that is really the only thing you did, then I think this is either a bug or a very unconventional choice on the part of Mathworks. I did this same style plot in R (using the psych library), and the output as you expect it -- with labeling of the figures aligned for both the histogram and the scatterplot. I can't think of a reason to not do it that way.

So, if you are sure that you have not adjusted the scatterplot axes after running the above commands, then I would submit a bug report, including your data and code.

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JT Yang 2019-7-14

Hi, thanks cyclist, I am also testing with Python matplotlib, it seems fine to plot the same type plot.

I'm not sure whether it is a bug or design preference. But I think it is good to share.

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Answer 2

dpb 2019-7-13

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编辑：dpb 2019-7-13

在 MATLAB Online 中打开

It's a confusing labeling problem -- the ticks aren't actually the variables on the plot for the histogram but for the scatter plots -- the axes values are for the scatter plot in the upper right quadrant which is scatter(x(:,2),x(:,1)) while the lower left is scatter(x(:,1),x(:,2)).

So, the x-axes limits are for var2 which are bounded at -1; the labels have nothing to do with the histograms; only the scatter plots. TMW just placed the x-axis labels for all the suplots at the bottom instead of keeping them with their respective suplot locations.

If create a poor-man's copy...

subplot(2,2,1)
hist(MCMC(:,1),100)
subplot(2,2,2)
scatter(MCMC(:,2),MCMC(:,1))
ylim([0 0.025])
xlim([-1.105 -0.7])
subplot(2,2,3)
scatter(MCMC(:,1),MCMC(:,2))
xlim([0 0.025])
ylim([-1.105 -0.7])
subplot(2,2,4)
hist(MCMC(:,2),100)
xlim([-1.05 -0.75])

one gets

so, while perhaps confusing, looks like the data are in fact correct...I don't have the Econometrics TB so can't go in and query what the actual limits are on each subplot() but doing so will make things clear, I expect. I fiddled around to roughly approximate the appearance on the LRH one...that took some doing...what the logic is that created the actual limits would be interesting to go look at, perhaps.

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dpb 2019-7-14

编辑：dpb 2019-7-14

在 MATLAB Online 中打开

Wowsers!!! They went all out...

>> openfig('corrplot.fig')
Warning: Unable to load instances of class matlab.ui.controls.AxesToolbar into a heterogeneous array.  The definition of
...
ans = 
  Figure (2) with properties:
      Number: 2
        Name: ''
       Color: [0.9400 0.9400 0.9400]
    Position: [675 549 570 420]
       Units: 'pixels'
  Show all properties
>> hF=gcf;
>> hA=hF.Children
hA = 
  7×1 Axes array:
  Axes    (PlotMatrixHistAx)
  Axes    (PlotMatrixHistAx)
  Axes    (PlotMatrixScatterAx)
  Axes    (PlotMatrixScatterAx)
  Axes    (PlotMatrixScatterAx)
  Axes    (PlotMatrixScatterAx)
  Axes    (CorrPlot)
>> xl=get(hA,'XLim');
>> xl{:}
ans =
    0.0032    0.0280
ans =
   -1.0300   -0.7700
ans =
    0.0051    0.0261
ans =
   -1.1193   -0.7334
ans =
    0.0051    0.0261
ans =
   -1.1193   -0.7334
ans =
     0     1
>> 

Looks like they created an axes for each quadrant for starters and plotted scatter and then overlaid two additional axes for the two histograms on top...instead of just a simple four-axes subplot() thing.

But, you can see where they left the ranges after done by default...

I confirmed that axes 2 and 6 are the LRH corner by

text(hA(6),-1,-0.8,'SIX')
text(hA(2),-1,7000,'TWO')
hA(6).Color='none';
hA(2).Color='none';

which also reveals they drew a line on the scatter axes that seems to traverse the range of the scatter plot data--I don't understand the purpose for it to then hide it...

Curiouser and curiouser... :)

ADDENDUM:

It appears the line is plot() of the scatter data sorted by increasing x...for what purpose still escapes me--they could have easily found the ranges by simply using min()/max() unless were too lazy and letting the autoranger default the axis limits--but even that could be just the two extrema; why duplicate the whole data set yet again??? But no, that isn't it because the limits aren't even as would otherwise be and

>> hA(6).XLimMode
ans =
    'manual'
>> 

confirms that.

Bizarre.

JT Yang 2019-7-14

Hi, dpb. You are superb. I've never dive down so deep into plotting. Now I know how to get the xlim for all graphs. That will be helpful for get around.

dpb 2019-7-15

One additional note: The line for the diagonal axes that isn't shown is just the variable plotted against itself--the 'ii' case so it is simply a 45-degree line of the range of the variable. The just didn't bother to fix up the logic to not plot the i==j case but did all and then overwrote the diagonal with the histograms not bothering to delete() the extra axes/line.

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