Lesson 11 - Mathematical functions in Kotlin

Kotlin Basic constructs Mathematical functions in Kotlin

In the previous lesson, Multidimensional arrays in Kotlin, we introduced multidimensional arrays. Learning Kotlin actually starts from now on, however, this online course of the most basic constructs of the language will be finished today. I'm glad that we successfully got until here, the next online course will be about object oriented programming. We'll be creating really interesting applications and even one game. We'll end this course with a simple article about mathematical functions that will certainly come handy in our future programs.

The basic math functions in Kotlin are contained in the kotlin.math package. We've already encountered the sqrt() function to get the square root.

In the older versions of the language, math functions were called on the Math class, for example as Math.sqrt(24.0). Be sure to use the new notation instead where the functions are called independently.

Importing the kotlin.math library

To use the math functions we have to write this line at the top of our file:

import kotlin.math.*

Constants

We are provided with the following math constants: PI and E. PI is, of course, the number pi (3.1415...) and E is the Euler's number, ie. the base of natural logarithm (2.7182...).

print("Pi: ${PI}\ne: ${E}")

The output:

Pi: 3.141592653589793
e: 2.718281828459045

Available math functions

Now, let's describe the functions the library offers.

The input types support of the functions mentioned below varies. Some functions are defined for decimal numbers only and some only for, e.g. Double and Int, but don't support Float. We already know that when we write a function name and press Ctrl + Space, its overloads show up, i.e. the available ways to call the given function.

Let's say you want to use, for example, the pow() function, see below. For integers, it'd be necessary to cast these numbers to e.g. the Double type first. We can do this by typing (3 as Double).pow(2); this would convert the value of 3 to a decimal number first and then square it.

min(), max()

Let's start with the simple methods :) Both functions take two numbers of any data type as parameters (but both parameters has to be of the same type). The min() function returns the smallest number, the max() function returns the largest one.

round(), ceil(), floor() and truncate()

All these functions are related to rounding. round() takes a decimal number as a parameter and returns the rounded number of the Double or Float type in the way we learned in school (from 0.5 it rounds upwards, otherwise downwards). ceil() (ceiling) rounds always upwards and floor() rounds downwards no matter what. All these functions are expecting the Double or Float type.

We'll certainly be using round() very often. I practically used the other functions e.g. in determining the number of pages of a guestbook. When we've 33 comments and we print only 10 comments per page, they'll, therefore, occupy 3.3 pages. The result must be rounded up since there will be actually 4 pages.

If you think that floor() and truncate() do the same thing, think again! They behave differently for negative numbers. floor() rounds negative numbers down to the next "more negative" number, truncate() always rounds to zero when the input is negative.

We round decimal numbers and store them in Int variables like this:

var d = 2.72
var a: Int = round(d).toInt()

abs() and sign()

abs() takes any number of any type as a parameter and returns its absolute value. sign() takes a decimal number on the input and returns -1.0, 0.0, or 1.0 depending on the sign of the number (whether it's negative, zero, or positive).

sin(), cos(), tan()

The classic trigonometric functions, they all take an angle in radians as Double or Float as a parameter, remember they don't work with degrees. To convert degrees to radians we multiply them by * (PI / 180). The output is a decimal number again.

acos(), asin(), atan()

Again, the classic inverse trigonometric functions (arcus, sometimes cyclometric functions), which return the original angle according to the trigonometric value. The parameter is the value as a decimal number, the output is the angle in radians (also a decimal number). If we wish to have an angle in degrees, we have to divide the radians by / (180 / PI).

pow() and sqrt()

We don't call the pow() method globally, but we call it on the base which is Double or Int. As a parameter, it takes the exponent as Double or Int. If we wanted to calculate, for example, 23, the code would look like this:

println(2.0.pow(3))

Sqrt() is an abbreviation of SQuare RooT, which returns the square root of the number given as Double or Float.

print(sqrt(24.0))

exp(), log(), log10(), log2()

exp() returns the Euler's number raised to a given decimal exponent. log() returns the natural logarithm of a given decimal number. log10() then returns the decadic logarithm (the base is 10) of a given decimal number and log2() the logarithm with the base 2.

Hopefully, you noticed that the method list lacks any general root function. We, however, can calculate it using the functions kotlin.math provides us with.

We know that roots work like this: 3rd root of 8 = 8^(1/3). So we can write:

println(8.0.pow((1.0/3.0)))

Division

Programming languages often differ in how they perform the division of numbers. You need to be aware of these issues to avoid being, unpleasantly, surprised afterwards. Let's write a simple program:

val a = 5 / 2
val b = 5.0 / 2
val c = 5 / 2.0
val d = 5.0 / 2.0
// val e: Int = 5 / 2.0
// val f: Double = 5 / 2

print("$a\n$b\n$c\n$d")

We divide 5/2 for several times in the code, it is mathematically 2.5. Nonetheless, the results will not be the same in all cases. Can you guess what we'll get in each case? Go ahead, give it a try :)

The code wouldn't be compiled because of the lines with the e a f variables, which we commented. The problem is that in these cases the result is a decimal number which we're trying to store into an integer (Int) or we're storing an integer into Double. The program's output is as follows:

2
2.5
2.5
2.5

We see the result of this division is sometimes decimal and sometimes whole. If any of the numbers is decimal, the result is also always decimal. Two integers return always an integer. Keep in mind that if you compute the average and want a decimal result, at least one variable must be cast to a decimal number.

For example, the PHP language always returns the decimal result of the division. When you divide in different programming languages make sure you check how division works there first before you use it.

The remainder after division

In our applications, we often need the remainder after integer division (i.e. modulo). In our example 5/2, the integer result is 2 and modulo is 1 (what left over). Modulo is often used to determine whether a number is even (remainder of division by 2 is 0), if you want, for example, to draw a checkerboard and fill in the fields based on whether they are even or odd, calculate the deviance of your position from some square grid, and so on.

In Kotlin and C-like languages in general, modulo is a percent sign, i.e. %:

println(5 % 2) // Prints 1

Well, that's all I've got for you in this course. The course will continue in the section Basics of Object-Oriented Programming in Kotlin. Next time, we'll introduce the world of objects and understand a lot of things that remained unrevealed until now :) You should surely try the exercises, they contain some console stuff we haven't shown yet and other interesting projects.


 

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Article has been written for you by Samuel Kodytek
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