tailieunhanh - Basic Mathematics for Economists phần 10

Vì vậy, yêu cầu thuê xe trong khoảng thời gian 3 tuần trong ví dụ này có thể được đặt ra như ma trận trong đó mỗi hàng tương ứng với một kích thước của chiếc xe và mỗi cột tương ứng với một tuần. Hệ thống ký hiệu thông thường là để biểu thị các ma trận bằng một bức thư vốn in đậm, | Table Cars required Week 1 Week 2 Week 3 Compact 4 7 2 Intermediate 3 5 5 Large 12 9 5 People carrier 2 1 3 Luxury limousine 1 1 2 The total car hire bill for each week can then be calculated by multiplying the number of cars to be hired in each category by the corresponding price. A matrix is defined as an array of numbers or algebraic symbols set out in rows and columns. Therefore the car hire requirements for the 3-week period in this example can be set out as the matrix 4 7 2 3 5 5 A 12 9 5 2 1 3 1 1 2 where each row corresponds to a size of car and each column corresponds to a week. The usual notation system is to denote matrices by a capital letter in bold type as for matrix A above and to enclose the elements of a matrix in a set of squared brackets . . Matrices may also be specified with algebraic terms instead of numbers. Each entry is usually known as an element . The elements in each matrix must form a complete rectangle without any blank spaces. For example if there are 5 rows and 3 columns there must be 3 elements in each row and 5 elements in each column. An element may be zero though. The size of a matrix is called its order . The order is specified as number of rows X number of columns For example the matrix A above has 5 rows and 3 columns and so its order is 5 X 3. Matrices with only one column or row are known as vectors. These are usually represented by lower case letters in bold. For example the set of car rental prices we started this chapter with can be specified in as the 1 X 5 row vector p 139 160 205 340 430 and the car hire requirements in week 1 can be specified as the 5 X 1 column vector q 4 3 12 2 1 Matrix addition and subtraction Matrices that have the same order can be added together or subtracted. The addition or subtraction is performed on each of the corresponding elements. 1993 2003 Mike Rosser Example A retailer sells two products Q and R in two shops A and B. The number of items sold for the last 4 weeks in each .