MATLAB: Plots for unevenly distributed data

plottime

Hi,

I have an excel data which I am plotting in matlab as x- quantity= time and y-quantity= output. The y-quantity values are unevenly distributed w.r.t. x, i.e. the step size between x-quantity is not same. We know that matlab interpolates the unknown values between the known points to plot the graph.

How can I get these unknown values from the graph since I want the whole data to be equally distributed with specific step size.

Best Answer

You cannot get them from the plot, although you can calculate them.

To create a regularly-spaced time vector, used the linspace (link) function. To interpolate your y-values, use the interp1 (link) function.

Related Solutions

MATLAB: How to do 1-D interpolation with INTERP1 to find the nearest value to the left of the point (i.e. a zero-order hold curve) in MATLAB

The easiest and probably fastest way to achieve that is to use histc respectively histcounts.

Code example:

% create some example data
x=linspace(0,10,100);
y=sin(x);
% those are the query points
xi=linspace(1,9,50);
% use histcounts to get the locations
% of the nearest left neighbours
[~,~,bin]=histcounts(xi,x);
plot(x,y,'b*')
hold on
plot(xi,y(bin),'r*')

Note that you would have to add some guard when interpolating data points outside the range of x.

MATLAB: How do i find points where slope is zero.

If you want to use the gradient function to find the inflection points, and since you are dealing with finite-precision values, one approach would be to use linspace and interp1 to create a much higher resolution ‘time’ vector, and then interpolate the ‘angle’ vector to it.

Also, using a tolerance rather than a specific value here:

if slope_angle <= 1E-4

or something similar, might be more appropriate.

However, since you want to find the maxima and minima, the easiest approach would be to use the findpeaks function on the signal and its negative value (to find the minima), or the islocalmax and islocalmin functions to do the same.

It depends on what approach you want to take, and the constraints of your data and data processing.

Best Answer

Related Solutions

MATLAB: How to do 1-D interpolation with INTERP1 to find the nearest value to the left of the point (i.e. a zero-order hold curve) in MATLAB

MATLAB: How do i find points where slope is zero.

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