MATLAB Programming

11 Improving Performance and Memory Usage
As long as the contents of the array are not modified, there is no need to
store two copies of it. If you modify the array, then MATLAB does create a
separate array to hold the new values.
If you modify the array shown above by referencing it with variable A
(e.g., A(400,:) = 0), then MATLAB creates a copy of the array, modifies it
accordingly, and stores a pointer to the new array in A. Variable B continues
to point to the original array. If you modify the array by referencing it with
variable B (e.g., B(400,:) = 0), the same thing happens except that it is B
that points to the new array.
Array Headers
When you assign an array to a variable, MATLAB also stores information
about the array (such as data type and dimensions) in a separate piece of
memory called a header. For most arrays, the memory required to store the
header is insignificant. There is a small advantage though to storing large
data sets in a small number of large arrays as opposed to a large number of
small arrays, as the former configuration requires fewer array headers.
Structure and Cell Arrays. For structures and cell arrays, MATLAB creates
a header not only for each array, but also for each field of the structure and for
each cell of a cell array. Because of this, the amount of memory required to
store a structure or cell array depends not only on how much data it holds,
but also how it is constructed.
For example, a scalar structure array S1 having fields R, G, andB, eachfieldof
size 100-by-50, requires one array header to describe the overall structure,
and one header to describe each of the three field arrays, making a total of 4
array headers for the entire data structure:
S1.R(1:100,1:50)
S1.G(1:100,1:50)
S1.B(1:100,1:50)
On the other hand, a 100-by-50 structure array S2 inwhicheachelementhas
scalar fields R, G, andB requires one array header to describe the overall
structure, and one array header per field for each of the 5,000 elements of the
structure, making a total of 15,001 array headers for the entire data structure:
S2(1:100,1:50).R
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