Marker indices for a plot error

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])

[Robert Scott]

If i make the marker index 1 the error goes away.

Answer 1

[the cyclist]

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.

[Robert Scott]

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.

Answer 2

[Star Strider]

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.

.

[Robert Scott]

This is ambiguous , in order for this documentation to be correct the word absolutle needs to be added or the term sample index or vector index.

[Star Strider]

I will not argue with you about the MATLAB definitions.

If you want to put one point on a plot, either define it as such, or use the scatter function —

x = 0:0.1:2;
y = (x-1).^2;

figure
hp = plot(x, y, 'p-');
hp.MarkerIndices = 15;
hp.MarkerSize = 10;
hp.MarkerFaceColor = 'g';
grid

.

[Robert Scott]

and that is the issue, i dont know the index, i just no the x location I cant figure it out because the numbers im working with are very very small and im having a tuff time with truncating to do the math to figure out the actual index.

All i want to do is plot a point on a graph with an absolute X value and absolute y value

I also have tried to use create an x and y vector of the points i want to put a marker and plot that seperate but the issue is when i use plot twice once for the line and then again for the markers it overwrites it even with hold on

Your plot above works because you know the index.

I do not, i only know the absolute time

[Star Strider]

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.

.