b2sonicxh

2021-12-19

How many rows and columns are in an $m×n$ matrix or is it vice versa?

Karen Robbins

An m $×$ n matrix has m rows and n columns.

mauricio0815sh

I suggest you always to check the notation on the book which you are using. I found sometimes this notation with different meaning. In advanced books, for example. Even the notation for linear maps as matrices. Sometimes they write xT.

Jeffrey Jordon

Always check and make sure you have the right convention for the occasion. Usually m $×$ n is rows $×$ columns. I like to remember this as being in REVERSE alphabetical order - Rows by Columns, or R first then C. However, in Boyce & DiPrima's book "Elementary Differential Equations and Boundary Value Problems" an m $×$ n matrix has m vertical columns and n horizontal rows.

However, when addressing elements within a matrix, it's the opposite. The element "a sub i,j" references the element in the ith row and jth column. Lesson? Always check to make sure you have the correct convention!

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