# Basic matrices notation

• zoxee

#### zoxee

Just going over my linear algebra notes and I've forgotten the formal definition of ## \epsilon(i,j)_{rs} ##

I have written down ## \epsilon (i,j)_{rs} = \delta_{ir}\delta_{js} ## but I can't seem to remember what r and s represent. Also, I don't quite understand why it equals ## \delta_{ir}\delta_{js} ##. I have a book on order for linear algebra which will hopefully help me out, but I can't find anything online for it - so any help would be appreciated

hi zoxee! I have written down ## \epsilon (i,j)_{rs} = \delta_{ir}\delta_{js} ## but I can't seem to remember what r and s represent.

## \epsilon(i,j)## is a matrix

## \epsilon(i,j)_{rs} ## is the rth row sth column of that matrix Also, I don't quite understand why it equals ## \delta_{ir}\delta_{js} ##

that's the definition of the matrix ## \epsilon(i,j)##

afaik, ## \epsilon(i,j)## isn't important, there's no need to remember it …

if it comes up in an exam question, they'll give you that definition, and ask you questions about it​

Just going over my linear algebra notes and I've forgotten the formal definition of ## \epsilon(i,j)_{rs} ##

I have written down ## \epsilon (i,j)_{rs} = \delta_{ir}\delta_{js} ## but I can't seem to remember what r and s represent. Also, I don't quite understand why it equals ## \delta_{ir}\delta_{js} ##. I have a book on order for linear algebra which will hopefully help me out, but I can't find anything online for it - so any help would be appreciated

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I have a feeling your r and s are the dimensions of your matrix. ##\delta_{ij} ## is 1 when i = j and 0 otherwise.

Does that fit with what you remember?