HP 50G, Руководство пользователя

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Page 11-14
Function TRACE
Function TRACE calculates the trace of square matrix, defined as the sum of the
elements in its main diagonal, or
.
Examples:
For square matrices of higher order determinants can be calculated by using
smaller order determinant called cofactors. The general idea is to "expand"
a determinant of a n
×
n matrix (also referred to as a n
×
n determinant) into a
sum of the cofactors, which are (n-1)
×
(n-1) determinants, multiplied by the
elements of a single row or column, with alternating positive and negative
signs. This "expansion" is then carried to the next (lower) level, with
cofactors of order (n-2)
×
(n-2), and so on, until we are left only with a long
sum of 2
×
2 determinants. The 2
×
2 determinants are then calculated through
the method shown above.
The method of calculating a determinant by cofactor expansion is very
inefficient in the sense that it involves a number of operations that grows very
fast as the size of the determinant increases. A more efficient method, and
the one preferred in numerical applications, is to use a result from Gaussian
elimination. The method of Gaussian elimination is used to solve systems of
linear equations. Details of this method are presented in a later part of this
chapter.
To refer to the determinant of a matrix A , we write det( A ). A singular matrix
has a determinant equal to zero.
∑
=
=
n
i
ii
a tr
1
) ( A