Apply function on several matrices without for loop

1 次查看（过去 30 天）
Guillaume
Guillaume 2017-10-9
评论： Guillaume 2017-10-9
Hi all,
I have hundred 3x3 rotation matrices stored in a 100x9 matrix. I would like to compute the corresponding rotation vectors using the Rodrigues convention. The desired output would be a 100x3 matrix.
Currently, I have written a function with a for loop that reads the 9 parameters of each rotation matrix line by line and fills in the corresponding rotation vector line by line.
function [rot_vectors] = rotationMatricesToVectors(rot_matrices)
nb_rotations = size(rot_matrices,1);
rot_vectors = zeros(nb_rotations,3);
for i = 1:nb_rotations
R = [...
rot_matrices(i,1) rot_matrices(i,2) rot_matrices(i,3);
rot_matrices(i,4) rot_matrices(i,5) rot_matrices(i,6);
rot_matrices(i,7) rot_matrices(i,8) rot_matrices(i,9)];
rot_vectors(i,:) = rotationMatrixToVector(R);
end
end
I was wondering if there is a more elegant way to write this function, in particular to avoid the for loop.
Thank you!
Guillaume
  4 个评论
显示 2更早的评论
Matt J
Matt J 2017-10-9
@Guillaume2,
Good point, although I don't think the transposition should matter, ultimately. The rotation axes are the same both for a rotation matrix R and its transpose.
Guillaume
Guillaume 2017-10-9
Hi Matt, Guillaume,
Thanks for the comments! As you suggested, I am going to change the indexing (column by column instead of row by row).
rotationMatrixToVector is actually a built-in function:
https://fr.mathworks.com/help/vision/ref/rotationmatrixtovector.html

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Matt J
Matt J 2017-10-9
编辑：Matt J 2017-10-9
I doubt this will be faster than a for loop, but it does get rid of it.
function [rot_vectors] = rotationMatricesToVectors(rot_matrices)
nb_rotations = size(rot_matrices,1);
Rstack=reshape(rot_matrices.',3,3,[]);
K=kron(speye(nb_rotations),ones(3));
K(K>0)=Rstack(:);
[v,~]=eigs(K,1);
rot_vectors=reshape(v,3,[]).';

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by