We called this number the determinant of A. It is
clear from this that we would like to have similar
result for bigger matrices (meaning higher orders).
There is similar notion of determinant for any
square matrix, which determines whether square
matrix is invertible or not. In order to generalize
such notion to higher orders, it is required to study
the determinant and see what kind of properties it
satisfies.
Notation
The following notation is used for the determinant:
ad cb
c d
a b
- = =
=
c d
a b
det
c d
a b
determinant of
1.2 Properties of the Determinant
(1) Any matrix A and its transpose have the
same determinant, meaning
det (A) = det(AT )
(2) The determinant of a triangular matrix is
the product of the entries on the diagonal,
that is
ad
c d
a
d
a b
= =
0
0
(3) If we interchange two rows, the
determinant of the new matrix is the
opposite of the old one, that is
a b
c d
c d
a b
= -
(4) If we multiply one row with a constant, the
determinant of the new matrix is the
determinant of the old one multiplied by
the constant, that is
kc kd
a b
c d
a b
k
c d
ka kb
= =
In particular, if all the entries in one row
are zero, then the determinant is zero.
(5) If we add one row to another one
multiplied by a constant, the determinant
of the new matrix is the same as the old
one, that is
c ka d kb
a b
c d
a b
c d
a kc b kd
+ +
= =
+ +
(6) We have
det (AB) = det(A) . det(B)
If A and B are similar, then
det (A) = det(B)
2. FORMING SINGULAR MATRIX
2.1 Special Properties
Let us consider following special properties
a11 + a22 – a21 = a12
a21 + a32 – a31 = a22
a12 + a23 – a22 = a13
a22 + a33 – a32 = a33
The determinant of any matrix constructed using
above properties is zero except matrix of order
(2 X 2) and (1 X 1) and the sum of elements in the
two diagonals is also equal.
2.2 Theorem
Theorem Any Matrix formed using the above
special properties is singular
Proof: Let us consider the 3 X 3matrix.
11 12 13
21 22 23
31 32 33
a a a
A a a a
a a a
=
From special properties (see Section. 2.1), we
derive
a11 – a12 = a21 – a22 = a31 – a32 (1)
a12 – a13 = a22 – a23 = a32 – a33 (2)
Subtracting second column from the first column
We get
11 12 12 13
21 22 22 23
31 32 32 33
_
_
_
A
a a a a
a a a a
a a a a
=
We called this number the determinant of A. It isclear from this that we would like to have similarresult for bigger matrices (meaning higher orders).There is similar notion of determinant for anysquare matrix, which determines whether squarematrix is invertible or not. In order to generalizesuch notion to higher orders, it is required to studythe determinant and see what kind of properties itsatisfies.NotationThe following notation is used for the determinant:ad cbc da b- = = = c da bdetc da bdeterminant of1.2 Properties of the Determinant(1) Any matrix A and its transpose have thesame determinant, meaningdet (A) = det(AT )(2) The determinant of a triangular matrix isthe product of the entries on the diagonal,that isadc dada b= =00(3) If we interchange two rows, thedeterminant of the new matrix is theopposite of the old one, that isa bc dc da b= -(4) If we multiply one row with a constant, thedeterminant of the new matrix is thedeterminant of the old one multiplied bythe constant, that iskc kda bc da bkc dka kb= =In particular, if all the entries in one roware zero, then the determinant is zero.(5) If we add one row to another onemultiplied by a constant, the determinantof the new matrix is the same as the oldone, that isc ka d kba bc da bc da kc b kd+ += =+ +(6) We havedet (AB) = det(A) . det(B)If A and B are similar, thendet (A) = det(B)2. FORMING SINGULAR MATRIX2.1 Special PropertiesLet us consider following special propertiesa11 + a22 – a21 = a12a21 + a32 – a31 = a22a12 + a23 – a22 = a13a22 + a33 – a32 = a33The determinant of any matrix constructed usingabove properties is zero except matrix of order(2 X 2) and (1 X 1) and the sum of elements in thetwo diagonals is also equal.2.2 TheoremTheorem Any Matrix formed using the abovespecial properties is singularProof: Let us consider the 3 X 3matrix.11 12 1321 22 2331 32 33a a aA a a aa a a = From special properties (see Section. 2.1), wederivea11 – a12 = a21 – a22 = a31 – a32 (1)a12 – a13 = a22 – a23 = a32 – a33 (2)Subtracting second column from the first columnWe get11 12 12 1321 22 22 2331 32 32 33___Aa a a aa a a aa a a a =
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