在不知道大小的情况下在Matlab中预分配空间? [英] Preallocating the space in Matlab without knowing the size?

问题描述

我正在通过在循环过程中串联每次迭代的结果来在Matlab中构造向量X.

I am constructing a vector X in Matlab by concatenating the outcomes of each iteration in a loop procedure.

我现在正在做的是

X=[];
for j=1:N
    %do something that delivers a vector A
    %X=[X;A]
end

不可能先验地预测A的大小.有什么方法可以预分配空间?

It is not possible to predict a priori the size of A. Is there any way in which I can preallocate the space?

推荐答案

可能的解决方案:

A=cell(1,N); %Pre-allocating A instead of X as a cell array
for k=1:N    %I changed the name of loop variable since `j` is reserved for imag numbers
  %Here I am generating a matrix of 5 columns and random number of rows. 
  %I kept number of columns to be constant (5) because you used X=[X;A] 
  %in the question which means number of columns will always be same
  A{k} =  rand(randi([1,10],1,1),5); %doing something that delivers a vector A   
end
X = vertcat(A{:}); 

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