Matlab 报错 Consider preallocating for speed

最新推荐文章于 2021-08-24 17:55:22 发布

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最新推荐文章于 2021-08-24 17:55:22 发布 · 2k 阅读

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当MATLAB变量在循环中通过赋值或拼接导致大小变化时，会出现'Consider preallocating for speed'的提示。这表明程序可能因频繁内存分配和复制而效率低下。解决方法是在循环开始前预分配数组大小，如使用zeros函数初始化。通过预分配，可以显著提升代码运行速度并避免警告。

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示例：

k=5;
a=zeros(k,k);
for m=1:k
    for n=1:k 
		a(m,n)=1/(m+n-1); 
    end
end
for i=1:1:10
    b(i)=i+20;
end

报错如下：

Explanation
The size of the indicated variable or array appears to be changing with each loop iteration. Commonly, this message appears because an array is growing by assignment or concatenation. Growing an array by assignment or concatenation can be expensive. For large arrays, MATLAB must allocate a new block of memory and copy the older array contents to the new array as it makes each assignment.
Programs that change the size of a variable in this way can spend most of their run time in this inefficient activity. There is also significant overhead in shrinking