MATLAB Programming

Resizing and Reshaping Matrices
The preferred method for sizing an array that is expected to grow over time
is to estimate the maximum possible size for the array, and preallocate this
amount of memory for it at the time the array is created. In this way, your
program performs one memory allocation that reserves one contiguous block.
The following command preallocates enough space for a 25,000 by 10,000
matrix, and initializes each element to zero:
A = zeros(25000, 10000);
Building a Preallocated Array
Once memory has been preallocated for the maximum estimated size of the
array, you can store your data in the array as you need it, each time appending
to the existing data. This example preallocates a large array, and then reads
blocks of data from a file into the array until it gets to the end of the file:
blocksize = 5000;
maxrows = 2500000; cols = 20;
rp = 1; % row pointer
% Preallocate A to its maximum possible size
A = zeros(maxrows, cols);
% Open the data file, saving the file pointer.
fid = fopen('statfile.dat', 'r');
while true
% Read from file into a cell array. Stop at EOF.
block = textscan(fid, '%n', blocksize*cols);
if isempty(block{1}) break, end;
% Convert cell array to matrix, reshape, place into A.
A(rp:rp+blocksize-1, 1:cols) = ...
reshape(cell2mat(block), blocksize, cols);
% Process the data in A.
evaluate_stats(A);
% User-defined function
% Update row pointer
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