read specific data from a given row and column from table

I have table of size 28000x3

and i want to biefuracte data which looks like this.

I am using slope condition to collect the data.

function bifercation(Data)

c = 1;

for i= c:length(Data.para)

find((Data.para(i+1)-Data.para(i)) / (Data.Time(i+1)-Data.Time(i)))

end

end

however; i am getting following errors.

Index exceeds the number of array elements. Index must not exceed 28000.

Error in tabular/dotParenReference (line 111)

b = b(rowIndices);

Error in bifercation (line 8)

find((Data.para(i+1)-Data.para(i)) / (Data.Time(i+1)-Data.Time(i)))

diffenrece between time is non zero throughout the period.

[AL]

function bifercation(Data)
c = 0;
para = [0 0];
l = size(Data,1);
for c1 = 1:9
    for i= c:l(1)
        array = find((Data.para(i+1)-Data.para(i)) / (Data.Time(i+1)-Data.Time(i)));
        if array ~= 0
            para(i,1) = Data(i,1);
            para(i,2) = Data(i,3);
        elseif array == 0
            c = i;
            break;
        else
            continue;
        end
    end    
end
end
Array indices must be positive integers or logical values.
Error in tabular/dotParenReference (line 111)
b = b(rowIndices);
Error in bifercation (line 7)
array = find((Data.Thrust_Force(i+1)-Data.Thrust_Force(i)) / (Data.Time(i+1)-Data.Time(i)));

updated code

Answer 1

[Mathieu NOE]

hello

maybe you need a function to give you start / stop time indexes based on threshold crossing

like this

clc
clearvars

% dummy data
n=1000;
x= 10*(0:n-1)/n;
y1 = sign(sin(2*x -0.5));
y2 = sin(x.^2 -0.5);

threshold = max(y1)/2; % half amplitude

[t0_pos1,s0_pos1,t0_neg1,s0_neg1]= crossing_V7(y1,x,threshold,'linear'); % positive (pos) and negative (neg) slope crossing points 
% ind => time index (samples)
% t0 => corresponding time (x) values 
% s0 => corresponding function (y) values , obviously they must be equal to "threshold"
[t0_pos2,s0_pos2,t0_neg2,s0_neg2]= crossing_V7(y2,x,threshold,'linear'); % positive (pos) and negative (neg) slope crossing points 


% periods
d1 = diff(t0_pos1)
period1 = [d1(1) d1];
d2 = diff(t0_pos2)
period2 = [d2(1) d2];

figure(1)
subplot(3,1,1),plot(x,y1,'b',t0_pos1,s0_pos1,'*r',t0_neg1,s0_neg1,'*g','linewidth',2,'markersize',12);grid on
legend('signal','signal positive slope crossing points','signal negative slope crossing points');
subplot(3,1,2),plot(x,y2,'b',t0_pos2,s0_pos2,'*r',t0_neg2,s0_neg2,'*g','linewidth',2,'markersize',12);grid on
legend('signal','signal positive slope crossing points','signal negative slope crossing points');
subplot(3,1,3),plot(t0_pos1,period1,t0_pos2,period2,'linewidth',2,'markersize',12);grid on
legend('signal 1 period','signal 2 period');



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [t0_pos,s0_pos,t0_neg,s0_neg] = crossing_V7(S,t,level,imeth)

% [ind,t0,s0,t0close,s0close] = crossing_V6(S,t,level,imeth,slope_sign) % older format

% CROSSING find the crossings of a given level of a signal
%   ind = CROSSING(S) returns an index vector ind, the signal
%   S crosses zero at ind or at between ind and ind+1
%   [ind,t0] = CROSSING(S,t) additionally returns a time
%   vector t0 of the zero crossings of the signal S. The crossing
%   times are linearly interpolated between the given times t
%   [ind,t0] = CROSSING(S,t,level) returns the crossings of the
%   given level instead of the zero crossings
%   ind = CROSSING(S,[],level) as above but without time interpolation
%   [ind,t0] = CROSSING(S,t,level,par) allows additional parameters
%   par = {'none'|'linear'}.
%	With interpolation turned off (par = 'none') this function always
%	returns the value left of the zero (the data point thats nearest
%   to the zero AND smaller than the zero crossing).
%


% check the number of input arguments
error(nargchk(1,4,nargin));

% check the time vector input for consistency
if nargin < 2 | isempty(t)
	% if no time vector is given, use the index vector as time
    t = 1:length(S);
elseif length(t) ~= length(S)
	% if S and t are not of the same length, throw an error
    error('t and S must be of identical length!');    
end

% check the level input
if nargin < 3
	% set standard value 0, if level is not given
    level = 0;
end

% check interpolation method input
if nargin < 4
    imeth = 'linear';
end


% make row vectors
t = t(:)';
S = S(:)';

% always search for zeros. So if we want the crossing of 
% any other threshold value "level", we subtract it from
% the values and search for zeros.
S   = S - level;

% first look for exact zeros
ind0 = find( S == 0 ); 

% then look for zero crossings between data points
S1 = S(1:end-1) .* S(2:end);
ind1 = find( S1 < 0 );

% bring exact zeros and "in-between" zeros together 
ind = sort([ind0 ind1]);

% and pick the associated time values
t0 = t(ind); 
s0 = S(ind);

if ~isempty(ind)

    if strcmp(imeth,'linear')
        % linear interpolation of crossing
        for ii=1:length(t0)
            %if abs(S(ind(ii))) >= eps(S(ind(ii)))    % MATLAB V7 et +
            if abs(S(ind(ii))) >= eps*abs(S(ind(ii)))    % MATLAB V6 et -    EPS * ABS(X)

                % interpolate only when data point is not already zero
                NUM = (t(ind(ii)+1) - t(ind(ii)));
                DEN = (S(ind(ii)+1) - S(ind(ii)));
                slope =  NUM / DEN;
                slope_sign(ii) = sign(slope);
                t0(ii) = t0(ii) - S(ind(ii)) * slope;
                s0(ii) = level;
            end
        end
    end

    % extract the positive slope crossing points 
    ind_pos = find(sign(slope_sign)>0);
    t0_pos = t0(ind_pos);
    s0_pos = s0(ind_pos);

    % extract the negative slope crossing points 
    ind_neg = find(sign(slope_sign)<0);
    t0_neg = t0(ind_neg);
    s0_neg = s0(ind_neg);

else

    % empty output
    ind_pos = [];
    t0_pos = [];
    s0_pos = [];
    ind_neg = [];
    t0_neg = [];
    s0_neg = [];
    
end

end

[Mathieu NOE]

hello

problem solved ?

tx

[AL]

Extremely sorry for response, Thank you so much for youe efforts, with your help and using concept explained by you was really helpful and solved my doubt. once again I really appriciate your efforts. Thank you so much. Have a wonderful weekend.

[Mathieu NOE]

Glad I could help

have a great day !