Chapter 8, Problem 8.1PE

(Sum elements column by column) Write a method that returns the sum of all the elements in a specified column in a matrix using the following header:

public static double sumColumn(double[][] m, int columnIndex)

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

Program Plan Intro

Sum of elements column by column

Program Plan:

• Include the “Scanner” package to get input values from user.
• Define the class named “Test”.
  • Define the main method.
    • Define the object “obj” for “Scanner” class to get input.
    • Declare the multi-dimensional array named “array”, and prompt the user to get array input.
    • Define the “for” loops, that get the input values for the variable “array”.
    • Define the “for” loop, that call the method “sumColumn()” with two arguments, they are array and index of array.
  • Define the method named “sumColumn()” with two arguments. One is a array variable “m” in type of “double” and another one is “columnIndex” with integer data type.
    • Declare the variable “total” in type of “double” and initialize the variable with “0”.
    • Set the “for” loop, the loop executes from “0” to length of array “m”.
      • Add the column values and store it into the “total”.
      • Return the value of “total”.

Program Description Answer

The following JAVA code is to sum the elements of array column by column using the method “sumColumn(double[][] m, int columnIndex)”.

Explanation of Solution

Program:

//Insert package

import java.util.Scanner;

//Class definition

public class Test

{

//Main method

public static void main(String[] args)

{

//Assign the object for "Scanner" class

Scanner obj = new Scanner(System.in);

//Print statement

System.out.print("Enter a 3 by 4 matrix row by row: ");

//Declaration of variable

double[][] array = new double[3][4];

//Outer loop

for (int i = 0; i < array.length; i++)

//Inner Loop

for (int j = 0; j <array[i].length; j++)

//Get input from user

array[i][j] = obj.nextDouble();

//Loop

for (int j = 0; j < array[0].length; j++)

{

//Print statement with function call

System.out.println("Sum of the elements at column " + j + " is " + sumColumn(array, j));     

}

}

//Function definition

public static double sumColumn(double[][] m, int columnIndex)

{

//Declaration of variable

double total = 0;

//Loop

for (int i = 0; i < m.length; i++)

//Add  the array values into variable

total += m[i][columnIndex];

//Return statement

return total;

}

}

Sample Output

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