Matrix Elements VB-800 Instrukcja Użytkownika Pobierz pdf (Strona 49)

A2.5 Ox exported mathematics functions 41

printf("error: allocation failed!");

MatZero(m, 3, 3); /* set m to 0 */

MatZero(&v, 1, 3); /* set v to 0 */

for (i = 0; i < 3; ++i) /* set both to 1 */

{ for (j = 0; j < 3; ++j)

m[i][j] = 1;

v[i] = 1;

}

/* ... do more work */

MatFree(m2, 3, 3); /* done: free memory */

free(v);

Note that the memory of a matrix is owned by the original matrix. It is NOT safe to

exchange rowsby swapping pointers. Rows also cannot be exchangedbetween different

matrices; instead the elements must be copied from one row to the other. Columns have

to be done element by element as well.

As a ﬁnal example, we show how to deﬁne a matrix which points to part of another

matrix. For example, to set up a matrix which points to the 2 by 2 lower right block in

m, allocate the pointers to rows:

MATRIX m2 = MatAlloc(2, 0);

m2[0] = &m[1][1];

m2[1] = &m[2][1];

// do work with m and m2, then free m2:

MatFree(m2, 2, 0);

Again note that the memory of the elements is still owned by m; deallocating m

deletes what m2 tries to point to.

When a language supports C-style DLLs, but not the pointer-to-pointer model used

in the MATRIX type, the following functions may be used to provide the necessary map-

ping:

MatAllocBlock function version of MatAlloc

MatCopyVecc store column-vectorized matrix in a MATRIX

MatCopyVecr store row-vectorized matrix in a MATRIX

MatFreeBlock function version of MatFree

MatGetAt get an element in a MATRIX

MatSetAt set an element in a MATRIX

VeccCopyMat store a MATRIX as a column vector

VecrCopyMat store a MATRIX as a row vector

1 2 ... 44 45 46 47 48 49 50 51 52 53 54 ... 171 172

Brak uwag

Matrix Elements VB-800 Instrukcja Użytkownika Strona 49