# Linear Dependence

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## linear dependence

[′lin·ē·ər di′pen·dəns]**v**, …,

**v**

_{n }in a vector space for which there exists a linear combination such that

*a*

_{1}

**v**

_{1}+ ··· +

*a*

_{n }

**v**

_{n }= 0, and at least one of the scalars

*a*

_{i }is not zero.

*The Great Soviet Encyclopedia*(1979). It might be outdated or ideologically biased.

## Linear Dependence

(mathematics), a relationship of the form

(*) C_{1}u_{1} + C_{2}u_{2} + ... + C_{n}u_{n} = 0

where *C*_{1}, *C*_{2},..., *C*_{n} are numbers, at least one of which is not zero, and *u*_{1}, *u*_{2},..., *u*_{n} are various mathematical objects for which the operations of addition and multiplication by a number are defined. The dependence relation (*) is said to be linear in the objects *u*_{1}, *u*_{2},..., *u*_{n}, since each of them enters (*) linearly, that is, the degree of each *u _{i}* in (*) is one. The equality sign in the above relation may have various meanings and its sense must be specified in each particular case.

The concept of linear dependence is used in many branches of mathematics. We may thus speak, for example, of linear dependence between vectors, between functions of one or several variables, and between elements of a vector space. If the objects *u*_{1}, *u*_{2},..., *u*_{n} are connected by a relation of linear dependence, then we say that they are linearly dependent. In the opposite case we say that they are linearly independent. If the objects *u*_{1}, *u*_{2},..., *u*_{n} are linearly dependent, then at least one of them is a linear combination of the others, that is,

*u*_{i} = α_{1}*u*_{1} + ... + α_{i - 1}*u*_{i-1} + α_{i + 1}*u*_{i + 1} + ... + α_{n}*u*_{n}

Continuous functions of one variable

*u*_{1} = ϕ_{1}(x), *u*_{2} = ϕ_{2}(x), . . ., *u*_{n} = ϕ_{n} (*x*)

are said to be linearly dependent if they are connected by a relation of the form (*), in which the equality sign is understood as an identity in *x.* In order for the functions Φ_{1}(x), Φ_{2}(x), . . ., Φ_{n}(x) defined on an interval *a* ≤ *x* ≤ *b* to be linearly dependent, it is necessary and sufficient that their Gramian vanish, the Gramian in this case being the determinant

Where

However, if the functions Φ_{1}(x), Φ_{2}(x),..., Φ_{n}(x) are solutions of a linear differential equation, then they are linearly dependent if and only if their Wronskian vanishes at at least one point.

Linear forms in *M* variables

*u*_{i} = *a*_{i 1}*x*_{1} + *a*_{i 2}*x*_{2} + ... + *a*_{im}*x*_{m}*i* = 1, 2,..., *n*

are said to be linearly dependent if they are connected by a relation of the form (*), in which the equality sign is understood as an identity in all the variables *x*_{1}, *x*_{2},..., *x*_{m}. In order for *n* linear forms in *n* variables to be linearly dependent, it is necessary and sufficient that the following determinant vanish: