How I can optimize my code for a stack construct?

In reality I have nine variables with scalar values. For them, I have built a stack construct (last in first out) with following logic: push (only for three variabled from nine, as an example)

stack(end+1:end+3) = [value1, value2, value3];

read and pop is

value3 = stack(end); stack = [];
value2 = stack(end); stack = [];
value1 = stack(end); stack = [];

In my script I call these code lines over 8 million time each and that is why I wish the time could be less. Can you help me to optimize the code lines and decrease the speed?

Answer 1

[Rik]

Dynamically growing a variable is generally slow, because Matlab needs to copy the entire array.

You could pre-allocate a stack and use a counter to keep track of the position in the stack.

[Nazar Adamchuk]

I am not copying the array, I am appending the elements to the array. That would be copying:

stack = [stack value1 value2 value3]

[Rik]

Matlab is copying the array for you: if you add an element to a vector Matlab will allocate a new block of memory, copy all the data (appending your new elements), and free the old memory blocks.

%these two operations are the exact same:
stack(end+1:end+3) = [value1, value2, value3];
stack = [stack, value1, value2, value3];