How to avoid this problem "consider preallocating the memory .for speed" in the below sample code

3 views (last 30 days)
The code is like this
m = [];
for k= 1:1:142
if(k >= 142)
if x(k)== [5];
mm = horzcat(mm,xx);
elseif (x(k+1) >= 20)
bb = 10- lj1 ;
cc = dec2bin(bb,3)-'0';
mm = horzcat(mm,cc);
elseif (x(k+2) >= 10)
cc = dec2bin(bb,3)-'0';
mm = horzcat(mm,cc);
how the preallocation of 'mm' can be done to increase the speed of execution. Kindly suggest
Steven Lord
Steven Lord on 14 Sep 2017
Can you explain the purpose of your code in words? If we know the underlying problem you're trying to solve, we may be able to suggest an alternative approach that avoids growing memory each time through the loop (potentially by avoiding the loop entirely!)

Sign in to comment.

Answers (2)

Stalin Samuel
Stalin Samuel on 14 Sep 2017
Refer the below url which has example of Preallocation
  1. pre-allocate memory when using MATLAB
  2. Preallocation

KSSV on 14 Sep 2017
If you are aware of the dimensions of the allocation preallcoate it using:
x = zeros(m,n) ;
If you are not aware of dimensions, and you know that it is either a row or a column vector:
x = zeros([],n) ; % a row row vector
x = zeros(m,[]) ; % a column vector
If you are not sure of dimensions, allocate it as cell:
x = cell([],n) ;
x = cell(m,[]) ;

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!