# error in the process of symbol operation of the matrix

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Asymptote001 le 29 Mai 2023
Modifié(e) : John D'Errico le 29 Mai 2023
It is convenient to use symbol operation to explore the relationship during the multiplication of matrices. And here is my code.
clc;clear;
theta = sym('theta',[1,4])
d = sym('d',[1,4])
a = sym('a',[1,4])
alpha = sym('alpha',[1,4])
T = ones(4,4)
for i = 2:1:4
T = T*[cos(theta(i)) -sin(theta(i)) 0 a(i-1);
sin(theta(i))*cos(alpha(i-1)) cos(theta(i))*cos(alpha(i-1)) -sin(alpha(i-1)) -d(i)*sin(alpha(i-1));
sin(theta(i))*sin(alpha(i-1)) cos(theta(i))*sin(alpha(i-1)) cos(alpha(i-1)) d(i)*cos(alpha(i-1));
0 0 0 1];
end
T What is wrong with T?
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### Réponses (2)

Matt J le 29 Mai 2023
Modifié(e) : Matt J le 29 Mai 2023
Nothing is wrong with T, though possibly you didn't scroll down far enough to see the definitions of all the sigmas.
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John D'Errico le 29 Mai 2023
Modifié(e) : John D'Errico le 29 Mai 2023
I would specuulate the issue is that T ends up as a rank 1 matrix, which it MUST, since T starts out as a rank 1 matrix, as ones(4).

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John D'Errico le 29 Mai 2023
Modifié(e) : John D'Errico le 29 Mai 2023
Why do you think there is something wrong with T? We don't know why you wrote this code. It computes what you told MATLAB to compute.
T is displayed there TWICE. The first time it is an array of all ones. A BAD IDEA. I think you wanted T to start as an IDENTITY matrix, not a matrix of all ones.
help eye
EYE Identity matrix. EYE(N) is the N-by-N identity matrix. EYE(M,N) or EYE([M,N]) is an M-by-N matrix with 1's on the diagonal and zeros elsewhere. EYE(SIZE(A)) is the same size as A. EYE with no arguments is the scalar 1. EYE(..., CLASSNAME) is a matrix with ones of class specified by CLASSNAME on the diagonal and zeros elsewhere. EYE(..., 'like', Y) is an identity matrix with the same data type, sparsity, and complexity (real or complex) as the numeric variable Y. Note: The size inputs M and N should be nonnegative integers. Negative integers are treated as 0. Example: x = eye(2,3,'int8'); See also SPEYE, ONES, ZEROS, RAND, RANDN. Documentation for eye doc eye Other uses of eye codistributed/eye codistributor2dbc/eye fixedpoint/eye codistributor1d/eye distributed/eye gpuArray/eye
The point is, if you are looking at this as a sequence of rotations, then you need to start with an identity matrix.
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