# The basis of a matrix

• Jan 8th 2012, 08:11 PM
ramakazi
The basis of a matrix
Hey guys.

I can calculate the basis of a matrix, but I'm a little unsure as to what they are asking here, if you could provide a bit of insight that would be awesome :)

Given that A represents all the the vectors in R3, and A = {(a,b,c): c = a – b and a, b, c R}.

Now if I don't have actual values, other than what's given above. What should I say for the basis for A and what is the dimension of A?

Thanks
• Jan 9th 2012, 04:18 AM
Deveno
Re: The basis of a matrix
not to be too nit-picky, but matrices don't "have bases". the column spaces or row spaces of matrices have bases. a basis is a generating set for a vector space, a matrix is just an array of numbers. in fact, a basis is a certain KIND of generating set, a minimal, or linearly independent one (linear dependence means that one or more elements of a set of vectors is redundant, we don't actually need it to recover the whole space. for example, {(1,0),(0,1),(1,1)} is redundant, we don't need (1,1) because we can recover it as (1,0) + (0,1)).

clearly, A does NOT "represent" ALL of R3, it is just some PART of R3. what we want to do is figure out "how big a part"?

one thing we can do, straight-away, is re-write A as:

A = {(a,b,c) in R3: c = a - b} = {(a,b,a-b): a,b in R}.

we can further re-write this as (a,b,a-b) = a(1,0,1) + b(0,1,-1), which suggests that A = span({(1,0,1),(0,1,-1)}).

of course, you haven't yet shown that A is, in fact, a vector space (which you should do), but if it is, then showing {(1,0,1),(0,1,-1)} is a basis

boils down to showing it is a linearly independent set.