MATLAB - 如何声明一个 "row slots"的矩阵供我插入行？

Question

在每次迭代中，我将一行插入行号已预先确定的矩阵中。我当前的实现是

seqToBePutIntoMatrix = [1 2 3 4 5 6 7 8 9];
col_no = 3; % hence the matrix is 3x3
myMatrix = [];
for i = 1:col_no:length(seqToBePutIntoMatrix)
    myMatrix = [myMatrix; seqToBePutIntoMatrix(i:i+col_no-1)];
end

MATLAB 向我建议

The variable myMatrix appears to change size in every loop iteration. Consider preallocation for speed.

我正在认真考虑它的建议，并希望预分配这样一个 3 行的空矩阵，并在每次迭代中插入一行。我试过这个:

seqToBePutIntoMatrix = [1 2 3 4 5 6 7 8 9];
col_no = 3; % hence the matrix is 3x3
myMatrix = [];
j = 1;
for i = 1:col_no:length(seqToBePutIntoMatrix)
    myMatrix(j) = seqToBePutIntoMatrix(i:i+col_no-1);
    j = j+1；
end

但是，这是行不通的。我怎样才能让它发挥作用？

Answer 1

下标 myMatrix(j) 仅引用 myMatrix 的一个单个 元素。为了引用整行，您需要

myMatrix(j,:) = seqToBePutIntoMatrix(i:i+col_no-1);

此外，您需要在 开始 for 循环

之前预先分配一个 3×3 矩阵

我的矩阵 = zeros(3,3);

附言，
最好not to use i and j as variable names in Matlab .