O'Reilly logo

Advanced Perl Programming by Sriram Srinivasan

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Example: Matrices

Before we embark on this example, you must know that if you really want a good efficient implementation of matrices, you should check out the PDL module (Perl Data Language) from CPAN.

To gain a better understanding of different matrix representations, we will write routines to construct these structures from a data file and to multiply two matrices. The file is formatted as follows:

MAT1
1  2  4
10 30 0

MAT2
5  6 
1  10

Each matrix has a label and some data. We use these labels to create global variables with the corresponding names (@MAT1 and @MAT2).

An array of arrays is the most intuitive representation for a matrix in Perl, since there is no direct support for two-dimensional arrays:

@matrix = (
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
); 
# Change 6, the element at row  1, column 2 to 100
$matrix[1][2] = 100;

Note that @matrix is a simple array whose elements happen to be references to anonymous arrays. Further, recall that $matrix[1][2] is a simpler way of saying $matrix[1]->[2].

Example 2.1 reads the file and creates the array of arrays structure for each matrix. Pay particular attention to the push statement (highlighted); it uses the symbolic reference facility to create variables (@{$matrix_name}) and appends a reference to a new row in every iteration. We are assured of newly allocated rows in every iteration because @row is local to that block, and when the if statement is done, its contents live on because we squirrel away a reference to the array’s value. (Recall ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required