# Marker indices for a plot error

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Robert Scott on 15 Aug 2021
Commented: Star Strider on 15 Aug 2021
So for whatever reason matlab will not allow me to make a marker index of less then 1. I get an error of
"Value must be a vector of positive integers."
I dont understand the problem. The plot has an x axis scale of very small numbers like .00001-.0001
So naturally my markers must be in that range.
Does anyone know why im getting this error?
plot(time_stamps,smooth(data(1:end,k)),'MarkerIndices',[.01])
##### 1 CommentShowHide None
Robert Scott on 15 Aug 2021
If i make the marker index 1 the error goes away.

the cyclist on 15 Aug 2021
The MarkerIndices Name-Value pair is expecting the indices of the data points (e.g. the 1st, 5th, and 10th data point) to place the markers, not the values of those data points.
You might want to use the XTick property of the axes instead.
##### 1 CommentShowHide None
Robert Scott on 15 Aug 2021
This is just rediculous.
Now xticks is telling me the indices must be increasing.
Who cares if they are increasing. All i want to do is put a "dot" on a point on a plot.
when thigns like min and max come back i have no idea if one index will be greater then the other.
Mathworks needs to significantly rethink the constraints on some of these elementry functions.

Star Strider on 15 Aug 2021
From the documentation on MarkerIndices:
Indices of data points at which to display markers, specified as a vector of positive integers
and 0.01 is not an integer.
.
Star Strider on 15 Aug 2021
In that situation, and you want to put it at a x-value of 0.01, use interp1 and tthe x-values to find the y-values for the markers —
x = -0.5:0.13:2.5;
y = (x-1).^2;
figure
plot(x, y)
xp = 0.01;
yp = interp1(x, y, xp);
hold on
hp = plot(xp, yp, 'p');
hold off
hp.MarkerSize = 10;
hp.MarkerFaceColor = 'g';
grid
If you have the y-values and want to find the x-values, this becomes a bit more complicated, however otherwise straightforward.
.

R2020b

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