Is it possible to obtain polynomial function (equation) or curve fit function from saved (plotted) dataset array?

Hello.

First of all, sorry if this question might sound simple and silly. This is my first attempt to involve this comunity. I'm new with Matlab, hence I appriciate a lot if someone able to guide me on this. Thank you.

As mentioned above, I have a set of data in array (voltage, time) from a simulink simulation. The data been log from a scope. I try to look into almost similar question of mine in this forum, however most of the answers provided are not for dataset array input. I try to use the suggested method with array type data and obviously its will be error. Here some on my code to give a brief idea on what I'm working on.

%% 1. For Volatge Measurement
n = 0;
MinRint = 0.00889;
figure('Name','Data Plot of Change of Internal Resistance over Voltage Measurement');
for n=1:30
    filename = sprintf('dataCRLS_IntRes_%d.mat',n);
    load(filename, 'data');
     
    txt = [sprintf('%.5f Ohm',MinRint)];
    plot(data(:,1), 'DisplayName',txt);   % Here is my voltage data stored
    title('Line Plot of Voltage and Discharge Time of Different Internal Resistance');
    xlabel('Time (seconds)') ;
    ylabel('Voltage (V)') ;
   
    %% Here is my attempt to obtain the polynomial function. 
    p = polyfit(data(:,1));                                                                  
    
    hold on
    MinRint = MinRint + IntResSamp;
end

[Walter Roberson]

When you say "dataset", do you mean something created with the older dataset() call from Statistics toolbox https://www.mathworks.com/help/stats/dataset.html which has been mostly replaced by table() objects in current code?

Your mention of Simulink leads me to suspect that you do not have dataset() objects. What you more likely have is a timeseries() object https://www.mathworks.com/help/matlab/time-series-objects.html as those are used a lot with Simulink.

[Syafiq Anwar]

Thank you sir for responding on my problem. I appriciate that.

First, i might be confuse in using the right term. Sorry for the confusion. Regarding to the "dataset" issue, actually i use simulink scope and save the logging data to the workspace. The logging type is in array table. Therefore, the format saved is ".mat" file.

The purpose of having the log data is to plot a graph that contain 30 sample (for example). Each of the line graph is different. Although there is curve fitting in Matlab, I'm not sure it is possible to perform simultaneously all the lines.

I just wonder if Matlab able to generate multiple line graphs by using "plot(data(:,n))" and calculate area under the graph by using "trapz(data(:,n))", hence it is possible to obtain sort of line function using the same array dataset.

[Walter Roberson]

Could you confirm that you are using a "To File" block https://www.mathworks.com/help/simulink/slref/tofile.html that is configured for "Array" output ?

If so, then

load_struct = load('YourMatFilename.mat');
fn = fieldnames(load_struct);
data = load_struct.(fn{1});   %extracts first variable in file, whatever its name
t = data(1,:);
u = data(2:end,:).';   %each variable is stored across row, transpose to make them down columns
plot(t, u);  %plot will make a distinct line for each _column_ of input
u_area = trapz(t, u);

u_area will now have one area for each logged signal, with the areas computed independently for each signal.

[Image Analyst]

Sayfiq, please attach dataCRLS_IntRes_1.mat and dataCRLS_IntRes_2.mat

[Syafiq Anwar]

Here is the attachment per request Sir. Inside the file contains:

• a - 3513x5 double type
• crls - 1x1 dataset
• data - 4501x5 double type
• sample_IntRes - 30x1 double type

there is 5 column. The first one is voltage, current, power, SOC and temperature respectively.

Thank you.