MULTIDIMENSIONAL ARRAYS - Introduction to Java Programming: Comprehensive Version - page 306

Write a test program that reads a 3-by-4 matrix and displays the sum of each
column. Here is a sample run:

Enter a 3-by-4 matrix row by row:
1.5 2 3 4
5.5 6 7 8
9.5 1 3 1
Sum of the elements at column 0 is 16.5
Sum of the elements at column 1 is 9.0
Sum of the elements at column 2 is 13.0
Sum of the elements at column 3 is 13.0

*8.2

( Sum the major diagonal in a matrix ) Write a method that sums all the numbers
in the major diagonal in an n * n matrix of double values using the following

header:

public static double sumMajorDiagonal( double [][] m)

Write a test program that reads a 4-by-4 matrix and displays the sum of all its
elements on the major diagonal. Here is a sample run:

Enter a 4-by-4 matrix row by row:
1 2 3 4.0
5 6.5 7 8
9 10 11 12
13 14 15 16
Sum of the elements in the major diagonal is 34.5

*8.3

( Sort students on grades ) Rewrite Listing 8.2, GradeExam.java, to display the
students in increasing order of the number of correct answers.

**8.4

( Compute the weekly hours for each employee ) Suppose the weekly hours for all
employees are stored in a two-dimensional array. Each row records an employ-
ee's seven-day work hours with seven columns. For example, the following
array stores the work hours for eight employees. Write a program that displays
employees and their total hours in decreasing order of the total hours.

Su M T W Th F Sa

Employee 0 2434588

Employee 1 7343344

Employee 2 3343322

Employee 3 9347341

Employee 4 3543638

Employee 5 3446344

Employee 6 3748384

Employee 7 6359279

8.5

( Algebra: add two matrices ) Write a method to add two matrices. The header of
the method is as follows:

public static double [][] addMatrix( double [][] a, double [][] b)