Matrix Basics
An m×n matrix has m rows and n columns.
| Row | Column |
|---|---|
 |  |
| m | n |
Now you know matrix dimensions you will understand 
This is a 3x4 matrix coz it has 3 rows and 4 columns
so. so horizontal = 1 row = m in mxn
An m×n matrix has m rows and n columns.
| Row | Column |
|---|---|
| |
| m | n |
Now you know matrix dimensions you will understand This is a 3x4 matrix coz it has 3 rows and 4 columns
so. so horizontal = 1 row = m in mxn