Definition of linear independence/dependence and examples
A set of $n$ vectors $\{ \mathbf{x}_{1}, \mathbf{x}_{2}, \cdots, \mathbf{x}_{n} \}$ is said to be
linearly independent
iff the equation
holds only when all the coeffients $c_{1}, c_{2}, \cdots, c_{n}$ are equal to zero, i.e.,
.
On the other hand,
a set of $n$ vectors
$\{ \mathbf{y}_{1}, \mathbf{y}_{2}, \cdots, \mathbf{y}_{n} \}$
is said to be
linearly dependent
iff the equation
holds and there exists non-zero coeffient $d_{i}$ for any $i$, i.e.,
($i = 1, 2, \cdots, n$.)
Below are a brief supplement and examples.
Explanation
Acoording to the above definition,
if a set of vectors
$\{ \mathbf{y}_{1}, \mathbf{y}_{2}, \cdots, \mathbf{y}_{n} \}$
is linearly dependent,
at least one vector in the vectors
can be represented by a linear combination of the remaining vectors.
For example,
if $d_{i} \neq 0$,
$\mathbf{y}_{i}$ can be represented as
.
On the other hand, if the vectors are linearly independent, such expression is not permitted.
Therefore,
a set of vectors is said to be linearly dependent
when at least one vector in the vectors can be represented by a linear combination of the remaining vectors.
On the other hand,
a set of vectors is said to be linearly independent
when any vector can not be represented by a linear combination of the remaining vectors.
Example 1:
A set of vectors
is
linearly independent,
because
if the equation
holds,
then
.
Example 2:
Let us investigate whether
a set of vectors
is linearly independent.
If the equation
holds,
the coefficients satisfy
.
The solution
is
, which is not non-zero.
In this way, there exists non-zero coefficient satisfying $(1)$.
Therefore,
the set of vectors
$
\{ \mathbf{x}_{1}, \mathbf{x}_{2}, \mathbf{x}_{3} \}
$
is linearly dependent.
Therefore at least one vector is represented by a linear combination of the other vectors.
For example,
$\mathbf{x}_{3}$ is represented as
.
Example 3:
Let us investigate a set of vectors
is linearly independent.
If the equation
holds,
then
the coeffients $c_{1},c_{2},c_{3}$, satisfy
.
From this,
we have
.
Therefore
$
\{\mathbf{x}_{1}, \mathbf{x}_{2}, \mathbf{x}_{3} \}
$
is linearly independent.