在犰狳图书馆中使用索引向量对矩阵进行索引 [英] Index A Matrix Using A Vector of Indices in Armadillo LIbrary

问题描述

我将Armadillo Cpp代码用于矩阵代数.我有一个特征向量矩阵E，我想按其特征值在向量d中进行排序.

I'm using the Armadillo Cpp code for matrix algebra. I have an Eigenvector matrix E that I want to sort by its eigenvalues in a vector d.

mat E;
vec d;
eig_sym(d,E,Rxx);


// Sort indices of eignen values / vectors
// based on decreasing real part of eigen values.
uvec order = sort_index(-d);

// Extract top eigen vectors.
E = E(span::all,order(1,nb_sources));

我在文档中找不到与这种索引相关的任何内容.使用向量进行索引是一个常见的要求，如果Armadillo中不存在索引，我会感到惊讶.

I couldn't find anything related to this kind of indexing in the documentation. Indexing using a vector is such a common requirement that I'd be surprised if it isn't present in Armadillo.

在犰狳中执行此操作的正确方法是什么?

What is the proper way to do this in Armadillo?

推荐答案

一种方法是

E = E.cols(order(span(0,nb_sources-1)));

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