How can I use cubic spline to smooth data and sketch graphs.

Hi.

I have large sets of data where I need to use cubic spline to apply smoothing and sketch the graph. In my data I need to find the average of total vertical electron content (VTEC) and come up with one hourly value using cubic spline and than sketch the against time for a period of 24hrs for every month. I'm new to matlab software and any help and suggestions is highly appriciated. Please find attached the set of sample data that i need to analyse for month of Feb. Thank you.

[John D'Errico]

You don't use a cubic spline to average data at a given point. You really want to do that BEFORE you use a cubic spline.

Next, a cubic spline is typically an INTERPOLATING spline, so it won't smooth your data. It will pass directly through the data points.

Finally, you did NOT attach any data. You attached a small PICTURE of your data, which is completely useless unless someone were to try to type in your complete data set. I hope they have very good eyesight if they do. Is there a good reason why you want to make it more difficult for someone to help you?

If you really want help, then it would be best if you actually attach the true data. Do so either by pasting in the data as text, or by attaching a .mat file. A spreadsheet is also acceptable, but it takes slightly more effort for someone to read it in, IF they were going to try to help you. Again, is there a good reason why you want to make it difficult to get timely help? Please edit your question, or attach your data to a comment on your question. (Do not answer your question with the data, as many seem to do.)

[Vikash Raj]

Appologies for any inconvenience. I have attached the spreadsheet file. Please suggest any suitable method to analyse this data set. Thank you.

Answer 1

[Mathieu NOE]

hello

example of smoothing done on L1 data - FYI -

clc
clearvars
T = readtable('Feb 2020_Elv 50+.csv');
[samples,col] = size(T);
x = (0:samples-1);
L1 = T.L1;
L1s = smoothdata(L1,'movmedian',17);

plot(x,L1,x,L1s)
legend('raw','smoothdata')

[Vikash Raj]

Thank you. The plots looks good.

What sets of code I can write to smooth the data after improting only Time and Absolute_ Vtec in matlab and than apply the smoothing as you have done above ? I was trying but getting an error. Im using R2015a version.

[Mathieu NOE]

hello

what is the error message ?

does R2015a have the smoothdata function ? there are some alternatives

[Vikash Raj]

the error is ''Undefined function or variable 'smoothdata' ''

It does not have smoothdata function. It only has "smooth" function.

[Mathieu NOE]

hello

this is an alternative using smoothn (from FEX : smoothn - File Exchange - MATLAB Central (mathworks.com) - attached also for convenience

plot is :

code :

clc
clearvars
T = readtable('Feb 2020_Elv 50+.csv');
[samples,col] = size(T);
x = (0:samples-1);
L1 = T.L1;
L1s = smoothn(L1,200,'robust');

plot(x,L1,x,L1s)
legend('raw','smoothn')

[Vikash Raj]

Hi,

Even smoothn returns the error.

[Mathieu NOE]

mamma mia !

what's wrong this time ?

what is the error message ?

[Vikash Raj]

Hi,

the error is ''Undefined function or variable 'smoothn';

[Vikash Raj]

Instead of using 'smoothdata' and 'smoothn' I have tried with 'smooth' it was not giving any error.

[Vikash Raj]

I was reading a journal article where it was suggested that Total electron data can be smooth using cubic smoothing spline (csaps). Any suggestions How I can impelement this. Thank you.

[Mathieu NOE]

hello

I sent yu in my previous post the infos about

it was also attached (again here)

hello

this is an alternative using smoothn (from FEX : smoothn - File Exchange - MATLAB Central (mathworks.com) - attached also for convenience

you have to save that function in your working directory or in your matlab path

[Mathieu NOE]

If you have the Curve fitting toolbox the csaps function (and others) are available

[Vikash Raj]

Thank you for your suggestions