Wednesday 15 February 2017

Is the zero element and zero vector the same thing in the context of Linear Independence?




Say..



A finite set of elements from a linear space are linearly independent if:




  1. Their trivial linear combination is equal to the zero element

  2. Their trivial linear combination is equal to the zero vector




I am not sure if statements 1 and 2 say the same thing.



I know that the zero element has the properties; for elements x and y of a linear space :



x + zero element = x



x + y = zero element



And I believe a zero vector would be an n tuple with only zero elements: (0,0,...,0)




Right now I believe they are the same thing in terms of properties that they have when talking about linear spaces and I think it is just different terminology.



But I also know from an example of a field with 2 elements (even and odd) that, even is the zero element in the field and it is not an n tuple with only zero elements.



As even + even = even and even + odd = odd


Answer



Both your definitions are wrong. It should be, if the set is $\{v_1,\ldots,v_k\}$,




$$\sum_{i=1}^k \lambda_iv_k=0 \;\Rightarrow\;\text{all $\lambda_i=0$.}$$





You are correct that the zero vector in $\mathbb{R}^n$ has exactly $n$ entries that are equal to the real number $0$.



Finally, the terms zero element and zero vector are often used interchangeably in this context.


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