How to cut the desired signal?

Hello All. I need your guidance on how can i cut the signal and keep my desired signal only. I have a physiological signal. I just want to keep the part of the signal when it goes up and remove the begining and the end of the signal. I am attaching the signal image and the code used to generate it. Could you please guide me how to do this or is there any code to do. Looking forward to hearing from you. Thanks

cd 'D:\Research\TFR classification\DATI'
filenames=dir('*.txt');
Fs=500;
TextSize=24;
time_FIF=zeros(1,length(filenames));

for i= 24 %length(filenames)
    %% Signal
    %close all
    
    fprintf(['\n\n\n *******************************************\n\n'...
        '         CODICE data set = ' filenames(i).name(1:end-4) '\n\n'...
        '         We are  assuming a sampling rate of 500 Hz\n\n'...
        ' *******************************************\n\n'])

    %% Import data from text file
opts = delimitedTextImportOptions("NumVariables", 25);

% Specify range and delimiter
opts.DataLines = [1, Inf];
opts.Delimiter = "\t";

% Specify column names and types
opts.VariableNames = ["Var1", "Var2", "Var3", "Var4", "Var5", "Var6", "Var7", "Var8", "Var9", "Var10", "Var11", "Var12", "Var13", "Var14", "Var15", "Var16", "Var17", "Var18", "Var19", "Var20", "Var21", "Var22", "Var23", "VarName24", "Var25"];
opts.SelectedVariableNames = "VarName24";
opts.VariableTypes = ["string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "string", "double", "string"];

% Specify file level properties
opts.ExtraColumnsRule = "ignore";
opts.EmptyLineRule = "read";

% Specify variable properties
opts = setvaropts(opts, ["Var1", "Var2", "Var3", "Var4", "Var5", "Var6", "Var7", "Var8", "Var9", "Var10", "Var11", "Var12", "Var13", "Var14", "Var15", "Var16", "Var17", "Var18", "Var19", "Var20", "Var21", "Var22", "Var23", "Var25"], "WhitespaceRule", "preserve");
opts = setvaropts(opts, ["Var1", "Var2", "Var3", "Var4", "Var5", "Var6", "Var7", "Var8", "Var9", "Var10", "Var11", "Var12", "Var13", "Var14", "Var15", "Var16", "Var17", "Var18", "Var19", "Var20", "Var21", "Var22", "Var23", "Var25"], "EmptyFieldRule", "auto");
opts = setvaropts(opts, "VarName24", "DecimalSeparator", ",");

% Import the data

s = readtable(filenames(i).name, opts);
s = table2array(s);
s = s(1420:3358);
%s = s(4.1*Fs:7.4*Fs);
%% Clear temporary variables
clear opts
%%    
    Fig=figure;
    plot((1:length(s))/Fs,s,'k')
    xlabel('time (s)')
    title(['Signal ' filenames(i).name(1:end-4)])
    set(gca,'fontsize', TextSize);
    set(Fig,'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);

[Mathieu NOE]

hello

can you share your data and be more precise what you consider the start (first kneeat 1.5 s ?) and stop (more difficult to guess) ?

[Muhammad Hammad Malik]

yes start at 1.5 s and stop around 2 or 2.5 s, except these i want to remove.

[Mathieu NOE]

well , the simplest approach is to define the time boundaries of the valid data to plot

assuming your data are t (time) and y (data), create the logical array idx :

% create dummy data
t = (0:0.25:4)

t = 1×17

0 0.2500 0.5000 0.7500 1.0000 1.2500 1.5000 1.7500 2.0000 2.2500 2.5000 2.7500 3.0000 3.2500 3.5000 3.7500 4.0000

y = zeros (size(t));
y(7:end) = 1-exp(-3*t(1:end-6));

% extract portion between 1.5 and 2.5 s
idx = (t>=1.5 & t <=2.5)

idx = 1×17 logical array
   0   0   0   0   0   0   1   1   1   1   1   0   0   0   0   0   0

plot(t,y,'b',t(idx),y(idx),'-*r');

[Muhammad Hammad Malik]

Thanks for the response. i also attached the code above which i am using to generate the signal. Kindly have a look into it.

Answer 1

[Fangjun Jiang]

In general,

t=0:0.1:3.5;
signal=0:35;
index=and(t>=1.5, t<=2.0);
new_t=t(index);
new_signal=signal(index);
plot(new_t, new_signal)

[Muhammad Hammad Malik]

Thanks for the answer. In addition i also attached the code, which i used to generate the signal. can you have a look into this, how i can rewrite. kindly respond. thanks