Matrix Elements VB-800 Instrukcja Użytkownika Pobierz pdf (Strona 48)

40 Appendix A2 Exported Function Summary

A2.5 Ox exported mathematics functions

A2.5.1 MATRIX and VECTOR types

This section documents the C functions exported from the OxWin DLL to perform

mathematical tasks. With the DLL installed, any C or C

function could call these

functions to perform a mathematical task. The primary purpose is, if you, for example,

wish to use some random numbers in your C extension to Ox. It is also possible to just

use these functions without using Ox at all.

To use any of the functions in this section, you need to include both jdtypes.h and

jdmath.h (in this order), e.g.

#include "/ox/dev/jdtypes.h"

#include "/ox/dev/jdmath.h"

Or, if you have set up the information for your compiler such that /ox/dev is in the

include search path:

#include "jdtypes.h"

#include "jdmath.h"

Several types are deﬁned in ox/dev/jdtypes.h, of which the most important are

MATRIX, VECTOR and bool.

The MATRIX type used in this library is a pointer to a column of pointers, each point-

ing to a row of doubles. A VECTOR is just a pointer to an array of doubles. In a MATRIX,

consecutive rows (the VECTORs) do occupy contiguous memory space (although that

would not be strictly necessary in this pointer to array of pointers model). Suppose m is

a 3 by 3 matrix, then the memory layout can be visualized as:

m −→ m[0]

m[0] −→ m[0][0], m[0][1], m[0][2] ﬁrst row

m[1] −→ m[1][0], m[1][1], m[1][2] second row

m[2] −→ m[2][0], m[2][1], m[2][2] third row

Matrices can be manipulated as follows, using the 3 × 3 matrix m:

• m[0] is a VECTOR,theﬁrstrowofm;

• &m[1] is a MATRIX, the last two rows of m;

• &m[1][1] is a VECTOR, the last two elements of the second row.

• &(&m[1])[1] is a MATRIX, the last two elements of the second row (this is only

a 1 row matrix, since there is no pointer to the third row).

A MATRIX is allocated by a call to MatAlloc and deallocated with MatFree.Fora

VECTOR the functions are VecAlloc and free, e.g.:

MATRIX m; VECTOR v; int i, j;

m = MatAlloc(3, 3);

v = VecAlloc(3);

if (!m || !v) /* yes: error exit */

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Matrix Elements VB-800 Instrukcja Użytkownika Strona 48