Simplify the following text for a Grade 5 native English-speaking person.
Original: We write to define an m Ã -- n matrix A with each entry in the matrix called a ` ij for all 1 â i â m and 1 â j â n.
Simplified: where 1 â i â m and 1 â j â p. For example ( the underlined entry 1 in the product is calculated as