Problems in for loop with cell array

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Hello everyone,
I'm trying to get the phase shift of a normal sine wave with different sine waves that were produced by a robot. Every run of the experiment has a different period, so its y=sine(factor * x). I used Crossing_V7 function that was given to me a few days ago. When I used it with only one robot sine wave it worked fine, but now I want to use it for all five attempts with different parameters and I get the error message, that the length is different. Does anyone of you see the mistake? I'm pretty new to cell array calculations.
clear;
factor = [0.25, 0.5, 1.0, 2.0, 4.0];
z_irl = cell(1,5);
irl = readtable("C:\Users\Bruce Rogers\Documents\RoboDK\halfpi\Roboterfahrten\RSI_Auswertung_halfpi\min_vel12_halfpi.txt");
z_irl_temp = irl{:,4};
z_irl{:,1} = z_irl_temp;
irl = readtable("C:\Users\Bruce Rogers\Documents\RoboDK\1pi\Roboterfahrten\RSI_Auswertung_1pi\min_vel12_1pi.txt");
z_irl_temp = irl{:,4};
z_irl{:,2} = z_irl_temp;
irl = readtable("C:\Users\Bruce Rogers\Documents\RoboDK\2pi\Roboterfahrten\RSI_Auswertung_2pi\min_vel12_2pi.txt");
z_irl_temp = irl{:,4};
z_irl{:,3} = z_irl_temp;
irl = readtable("C:\Users\Bruce Rogers\Documents\RoboDK\4pi\Roboterfahrten\RSI_Auswertung_4pi\min_vel12_4pi.txt");
z_irl_temp = irl{:,4};
z_irl{:,4} = z_irl_temp;
irl = readtable("C:\Users\Bruce Rogers\Documents\RoboDK\8pi\Roboterfahrten\RSI_Auswertung_8pi\min_vel12_8pi.txt");
z_irl_temp = irl{:,4};
z_irl{:,5} = z_irl_temp;
%%
for j = 1:length(factor)
z_irl = z_irl{1,j};
num_irl = numel(z_irl);
t = (1:num_irl)*0.004;
A = 50;
b = 10; %Durchgänge
ti = 0.004;
%x = zeros(length(z_irl));
x(:,j) = 0:ti:(1/factor(j))*10*pi;
y(:,j) = -A*sin(factor(j)*x) + 389.387;
%y(j) = y(j)';
num_th = numel(x);
T = (1:length(x))*ti;
threshold = 389.387; % your value here
[t0_pos1(:,j),s0_pos1(:,j),t0_neg1(:,j),s0_neg1(:,j)]= crossing_V7(y(:,j),T(:,j),threshold,'linear'); % positive (pos) and negative (neg) slope crossing points %%Here I get the error message
[t0_pos2(:,j),s0_pos2(:,j),t0_neg2(:,j),s0_neg2(:,j)]= crossing_V7(z_irl(:,j),t(:,j),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"
figure(7)
% plot(T,y,'g',t0_pos1,s0_pos1,'+g',t0_neg1,s0_neg1,'+g','linewidth',2,'markersize',12);grid on
% hold on
% plot(t,z_irl,'b',t0_pos2,s0_pos2,'+b',t0_neg2,s0_neg2,'+b','linewidth',2,'markersize',12);grid on
% hold off
% title('Nullstellen beider Wellen, Grün: Theorie, Blau: Realität')
% xlabel('time');
% ylabel('distance');
% time difference for positive slope crossing points
dt_pos_slope(j) = t0_pos1(j) - t0_pos2(j);
% time difference for negative slope crossing points
if numel(t0_neg1(j)) ~= 5
t0_neg1_temp(j) = 0.004;
t0_neg1(j) = [t0_neg1_temp(j),t0_neg1(j)];
end
if numel(t0_neg2(j)) ~= 5
t0_neg2_temp(j) = 0.004;
t0_neg2(j) = [t0_neg2_temp(j),t0_neg2(j)];
end
dt_neg_slope(j) = t0_neg1(j) - t0_neg2(j);
end
%%
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).
%
% [ind,t0,s0] = ... also returns the data vector corresponding to
% the t0 values.
%
% [ind,t0,s0,t0close,s0close] additionally returns the data points
% closest to a zero crossing in the arrays t0close and s0close.
%
% This version has been revised incorporating the good and valuable
% bugfixes given by users on Matlabcentral. Special thanks to
% Howard Fishman, Christian Rothleitner, Jonathan Kellogg, and
% Zach Lewis for their input.
% Steffen Brueckner, 2002-09-25
% Steffen Brueckner, 2007-08-27 revised version
% Copyright (c) Steffen Brueckner, 2002-2007
% brueckner@sbrs.net
% M Noe
% added positive or negative slope condition
% 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!'); %This is the error message I get
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 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);
end

Accepted Answer

David Hill
David Hill on 1 Jul 2021
Why not just use fit() function
x=0:.01:2*pi;
y=(5+.05*randn(size(x))).*sin((3+.05*randn(size(x))).*x);
f=fit(x',y','sin1');
period=f.b1;
  3 Comments
David Hill
David Hill on 1 Jul 2021
Edited: David Hill on 1 Jul 2021
To obtain the amplitude, period, and shift of each sine wave, just run the above. Not sure how your are storing your data for each sine wave (x,y).
for k=1:numOfsineWaves
f=fit(x{k}',y{k}','sin1');%assumed the sine waves are stored in cell arrays since the size varies
m(k,:)=[f.a1,f.b1,f.c1];%stores amplitude,period,shift in matrix for all sine waves
end
Bruce Rogers
Bruce Rogers on 2 Jul 2021
Now I get what you mean. Thanks David, it helped, but I used another method, because otherwise I would had to change too much on the program

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