PDL: an object‐oriented programming environment for econometrics
介绍PDL（Perl数据语言），一个免费跨平台的Perl扩展模块，提供类似Matlab和Gauss的数组操作功能，并包含计量经济学常用的数值计算例程。
PDL (for Perl data language) is a free, cross-platform, extension module that endows Perl with \ncapabilities analogous to those of interactive systems for array manipulation such as Matlab and \nGauss. PDL was founded by the astronomer Karl Glazebrook, and is an ongoing project that \ninvolves many Perl programmers. In Baiocchi (2003) it was shown how Perl can be used as a \n‘glue’ language to solve a variety of data-processing problems. By design, Perl is not suitable for \nefficient numerical computing. For instance, in Perl arrays can store any type of scalar, that can be \nboth numbers or strings. Moreover, the length of an array and the type of its elements can change \nduring program execution. This flexibility is achieved at the expense of efficiency, both in terms \nof speed and memory usage, by using pointers to scalars and late binding. \nPDL introduces a compactly stored multidimensional array data type that can be manipulated \nwith fast low-level languages like C, Fortran, or Perl itself. PDL provides the fundamental \noperations of numerical linear algebra. Various methods are available to create multidimensional \narrays from lists of numbers and other arrays. Several functions can be used to access elements \nand slices of arrays. Several operators to conveniently manipulate arrays, including array addition \nand multiplication, and relational operators are implemented. A print method for displaying arrays \nis also provided. \nFunctionality useful for econometricians is provided by specific PDL extension modules. \nAs an example, PDL modules provide routines for determinants, inverses and singular value \ndecomposition of matrices, numerical differentiation, integration, interpolation, multidimensional \nroot-finding, random number generation, nonlinear programming, polynomial fits to data, and fast \nFourier transforms. \nPDL’s source code, and binaries for the most popular Linux distributions and for the ActiveState \nWindows distribution of Perl, can be obtained from the official PDL site.1