# Creating a vector made of three different unit vectors

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alexandra ligeti el 28 de Jun. de 2021
Comentada: Mathieu NOE el 5 de Jul. de 2021
Good afternoon,
I have three different unit vectors (I, J, K) composed of [Ix, Iy, Iz], [Jx, Jy, Jz], and lastly [Kx, Ky, Kz]. Each in dimension of 6349X3. I would like to create a vector P1 in the from that P1 = [Ix Jx Kx
Iy Jy Ky
Iz Jz Kz ]
And P2 in the same format of P1 but has different values of I, J, K
I need to create this P1 and P2 vector in order to calculate the rotation matrix, [R] = [P2]T[P1]
How do I create P1 and P2 so that the P1 and P2 is in dimesion 3X3 and cycles through the first index to the last calculating the rotation vector for each index?
I tried creating a for loop, however I landed up getting a vector in dimesnions 6349X9.
Please let me know if you require any data, workspace or code for reference.
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Mathieu NOE el 28 de Jun. de 2021
hello Alexandra
see demo code below ; the matrixes P and R have size 3 x 3 x 6349 (iterations are in 3rd index)
% A = [Ix, Iy, Iz] dimension of 6349X3
% B = [Jx, Jy, Jz] dimension of 6349X3
% C = [Kx, Ky, Kz] dimension of 6349X3
% P1 = [Ix Jx Kx
% Iy Jy Ky
% Iz Jz Kz ];
% so P1 = [A' B' C'];
m = 6349;
n = 3;
A = rand(m,n);
B = rand(m,n);
C = rand(m,n);
T = eye(n,n);
for ci = 1:m
P1 = [A(ci,:)' B(ci,:)' C(ci,:)'];
P2 = P1; % dummy code => change the P2 computation as needed
R(:,:,ci) = P2*T*P1;
end
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Mathieu NOE el 5 de Jul. de 2021
hello Alexandra
tip of the day : zip all the data files in one zip so you use only 1 of the 10 files allowed per day. :)
Mathieu NOE el 5 de Jul. de 2021
hello again
so the NaN are generated here , because with the actual way to zero pad the data , these lines of code will do zero divided by zero , and this gives NaN
%% Unit vectors
junit_REFvec_4 = newSvec_4./(Mag_newSvec_4+eps);
iunit_REFvec_3 = newSvec_3./(Mag_newSvec_3+eps);
kunit_REFvec_1 = -newSvec_1./(Mag_newSvec_1+eps);
junit_Dvec_4_5 = newDvec_4_5./(Mag_newDvec_4_5+eps);
iunit_Dvec_3_5 = newDvec_3_5./(Mag_newDvec_3_5+eps);
kunit_Dvec_1_5 = -newDvec_1_5./(Mag_newDvec_1_5+eps);
one way is to add at the denominator a tiny non zero value (like eps = 2.2204e-16) so that the division gives zero instead of NaN
one other alternative is to zero padd the data after you have done the divisions , but that requires a bit reworking the entire code.
hope it helped
also I did modify a bit the end of your code as I prefer this way of managing the time vectors (and not manually put the amount of samples) :
%% Quick check of data
figure
close all
fs_vicon = 100;
fs_sensor = 50; %approximately 50HZ
dt_v = 1/fs_vicon;
dt_s = 1/fs_sensor;
% time_v = (0:dt_v:4860*dt_v);%+0.54;
time_v = (0:Vicmax-1)'*dt_v;;%+0.54;
% time_v = time_v';
% time_s = 0:dt_s:1996*dt_s; %MSmax
time_s = (0:MSmax-1)'*dt_s; %MSmax
% time_s = time_s';
plot(time_v,(alpha_5)');
hold on
plot(time_s, MS_5_Alignment);
hold on

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