Pre-allocate memory gives zeros all the time, how to avoid?

Question

want2know 2013-11-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/105221-pre-allocate-memory-gives-zeros-all-the-time-how-to-avoid

关闭： MATLAB Answer Bot 2021-8-20

In the beginning of a function, we have to pre-allocate memory by doing something like this: integ_signal=zeros(5,4);

Using the below code as an example, if I comment out this line: integ_signal=zeros(5,4);, I will get the desired answer which is 10.1 instead of 0.1. But, in Matlab Function block, I have to pre-allocate memory, how could I pre-allocate memory at the same time still won't assign zero to the integ_signal all the time?

integ_signal(1,1)=10;
integ_signal=zeros(5,4);
a=zeros(10);
arr=zeros(5,4);
count=2;
a=1;
integ_signal(count,1)=  integ_signal(count-1,1);
arr(count,1) = integ_signal(count,1); 
arr(count,1) = arr(count,1) + abs(I(1,a)-I(1,a+1));

(Desired answer, without pre-allocating memory) >> arr arr =

         0         0         0         0
   10.1000         0         0         0
         0         0         0         0
         0         0         0         0
         0         0         0         0

(Wrong answer, with pre-allocating memory) >> arr

    arr =
       0         0         0
1000         0         0         0
       0         0         0
       0         0         0
       0         0         0

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

此问题已关闭。

Answer 1

Azzi Abdelmalek 2013-11-7

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/105221-pre-allocate-memory-gives-zeros-all-the-time-how-to-avoid#answer_114445

在 MATLAB Online 中打开

In your Matlab function, declare a variable arr as persistent

persistent arr
if isempty(arr)
 arr=zeros(5,4)
end

You write

a=zeros(10),
a=1

The result is a=1 , then the line a=zeros(10) is unnecessary

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

want2know 2013-11-7

ok, i tried this in Matlab workspace, but I got this Error using persistent A PERSISTENT declaration is only allowed in a M-file function. So, I was thinking to try this in my m-file, but due to the error I posted earlier (<http://www.mathworks.co.uk/matlabcentral/answers/105217-subscripted-assignment-dimension-mismatch-size-1-x-1-size-1-x)>, I could not check the outcome of using persistent yet.