a little bug in function "plot/stem"

when you run code:

a = ones(1179080,1);

stem(a)

as shown in figure,you will find the x axis is constant at the end of data.

why?

[VBBV]

a = ones(1179080,1);
stem(a(1:100000:end))

[VBBV]

which version of Matlab are you using ? It seems to work fine

[weibo li]

a = ones(1179080,1);
stem(a)

you should run ”stem(a)“ instead of stem(a(1:100000:end))。Next, zoom into a(1179070:1179080) and insert cursor，you will see that the x-axis of cursor is wrong as following figure.

[VBBV]

The figure is displaying X scale numbers in exponential format. They are NOT constant but varying from 117967 to 119780. You need to change the display format for X axis ticks from exponential to integer or fixed point notation. Then it appearks OK,

[VBBV]

a = ones(1179080,1);
stem(a)
ax= gca;
% zoomed x -scale 
xlim([1179070 1179080]);
% use ticks 
xticks(1179070:1179080);
% then ticklabels 
xticklabels(string(1179070:1:1179080));
grid

[Adam Danz]

@VBBV, OP is referring to the x values shown in the data tips.

[VBBV]

It seems the DataTip property uses constant (same) values for every 5 units on X scale. E.g demonstration is shown below. When i use values between 1179070 & 1179075 it shows 1179070 but when i change values between 1179076 & 1179080 it displays 1179080. This is inline with that given in documentation page That means it creates a datatip at the nearest data point and perhaps the default property of datatip for plots in Matlab.

datatip(target,x,y) creates a data tip on the 2-D plotted data point specified by x and y. If you specify approximate coordinates, then datatip creates a data tip at the nearest data point.

v = 1179080;
a = ones(v,1);
s = stem(a);

xlim(v-[10,0])
ylim([0.9,1.1])

%
d = datatip(s,1179071,1); 
d.X % Confirms correct placement

ans = 1179071

datatip(s,1179073,1);
datatip(s,1179076,1);
datatip(s,1179080,1);

Answer 1

[Adam Danz]

Reproduce the problem

v = 1179080;
a = ones(v,1);
s = stem(a);

xlim(v-[10,0])
ylim([0.9,1.1])

d = datatip(s,1179071,1); 
d.X % Confirms correct placement

ans = 1179071

datatip(s,1179074,1);
datatip(s,1179077,1);

Cause

By default, the datatip format uses a compact floating point format %g. When converted to string,

str2double(sprintf('%g',1179072))
 ans
    = 1179070

Solution

If you know the data should display as signed integers, specify the format of the DataTipTemplate using dataTipTextRow.

figure()
s = stem(a);

xlim(v-[10,0])
ylim([0.9,1.1])

row = dataTipTextRow('X',1:numel(a),'%d');
s.DataTipTemplate.DataTipRows(1) = row;

datatip(s,1179071,1); 
datatip(s,1179074,1);
datatip(s,1179077,1);

[weibo li]

Well done! Thanks!