Efficient way of preallocating memory

Hello,

Just wondering is there a better way to preallocate memory for a bunch of 4D arrays. Because so far the way I am doing it, the code stops with the error- Out of memory.

The way I am doing it so far is below

Human_Data.Dimension_Vertical  =Size_Human_tmp22(1);    % = 256
Human_Data.Dimension_Horizontal=Size_Human_tmp22(2);    % = 256
Human_Data.Dimension_Slice     =Size_Human_tmp22(4);    % = 16
Human_Data.Dimension_Repitition=Size_Human_tmp22(3)/2;  % = 64
  Human_Data.Image_Matrix_Tag=single(zeros(Human_Data.Dimension_Vertical,Human_Data.Dimension_Horizontal, Human_Data.Dimension_Repitition, Human_Data.Dimension_Slice));
  Human_Data.Image_Matrix_Control=single(zeros(Human_Data.Dimension_Vertical,Human_Data.Dimension_Horizontal,Human_Data.Dimension_Repitition, Human_Data.Dimension_Slice));
  Human_Data.Image_Matrix_Control_Tag_Sub=single(zeros(Human_Data.Dimension_Vertical,Human_Data.Dimension_Horizontal,Human_Data.Dimension_Repitition,Human_Data.Dimension_Slice));
  Human_Data.Image_Matrix_Control_Tag_Avg=single(zeros(Human_Data.Dimension_Vertical,Human_Data.Dimension_Horizontal, Human_Data.Dimension_Repitition, Human_Data.Dimension_Slice));

so all the matrices look like 256 x 256 x 64 x 16

Thanks in advance!

Answer 1

[Sean de Wolski]

One thing is to use the class input to zeros so that the zero matrix is never created in double precision. As you have it right now:

single(zeros(10));

the matrix is first created in double precision and converted to single later.

zeros(10,10,'single');

avoids this.

Answer 2

[Walter Roberson]

Instead of single(zeros(P,Q,R,W)), use zeros(P,Q,R,W,'single')

Otherwise you are allocating double-precision values and then throwing away the half memory not needed for 'single'. When you use 'single' as an argument to zeros() then single precision will be allocated directly.

Note: each of your arrays is 256 megabytes when stored as single precision, so you need at least 1 gigabyte of free storage to hold all four arrays.

(By the way, you might want to change 'Repititon' to 'Repetition')