ðŸŽ‰ Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io ðŸŽ‰

# angelikatyborska's solution

## to Complex Numbers in the Erlang Track

Published at Dec 23 2019 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution was written.

A complex number is a number in the form `a + b * i` where `a` and `b` are real and `i` satisfies `i^2 = -1`.

`a` is called the real part and `b` is called the imaginary part of `z`. The conjugate of the number `a + b * i` is the number `a - b * i`. The absolute value of a complex number `z = a + b * i` is a real number `|z| = sqrt(a^2 + b^2)`. The square of the absolute value `|z|^2` is the result of multiplication of `z` by its complex conjugate.

The sum/difference of two complex numbers involves adding/subtracting their real and imaginary parts separately: `(a + i * b) + (c + i * d) = (a + c) + (b + d) * i`, `(a + i * b) - (c + i * d) = (a - c) + (b - d) * i`.

Multiplication result is by definition `(a + i * b) * (c + i * d) = (a * c - b * d) + (b * c + a * d) * i`.

The reciprocal of a non-zero complex number is `1 / (a + i * b) = a/(a^2 + b^2) - b/(a^2 + b^2) * i`.

Dividing a complex number `a + i * b` by another `c + i * d` gives: `(a + i * b) / (c + i * d) = (a * c + b * d)/(c^2 + d^2) + (b * c - a * d)/(c^2 + d^2) * i`.

Raising e to a complex exponent can be expressed as `e^(a + i * b) = e^a * e^(i * b)`, the last term of which is given by Euler's formula `e^(i * b) = cos(b) + i * sin(b)`.

Implement the following operations:

• addition, subtraction, multiplication and division of two complex numbers,
• conjugate, absolute value, exponent of a given complex number.

Assume the programming language you are using does not have an implementation of complex numbers.

You also need to implement a `equal/2` function. For this you can consider two numbers as equal, when the difference of each component is less than 0.005.

## Running tests

In order to run the tests, issue the following command from the exercise directory:

For running the tests provided, `rebar3` is used as it is the official build and dependency management tool for erlang now. Please refer to the tracks installation instructions on how to do that.

In order to run the tests, you can issue the following command from the exercise directory.

``````\$ rebar3 eunit
``````

## Questions?

For detailed information about the Erlang track, please refer to the help page on the Exercism site. This covers the basic information on setting up the development environment expected by the exercises.

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### complex_numbers_tests.erl

``````%% Based on canonical data version 1.3.0
%% https://github.com/exercism/problem-specifications/raw/master/exercises/complex-numbers/canonical-data.json
%% This file is automatically generated from the exercises canonical data.

-module(complex_numbers_tests).

-include_lib("erl_exercism/include/exercism.hrl").
-include_lib("eunit/include/eunit.hrl").

'1_real_part_of_a_purely_real_number_test'() ->
?assert(1 ==
complex_numbers:real(complex_numbers:new(1, 0))).

'2_real_part_of_a_purely_imaginary_number_test'() ->
?assert(0 ==
complex_numbers:real(complex_numbers:new(0, 1))).

'3_real_part_of_a_number_with_real_and_imaginary_part_test'() ->
?assert(1 ==
complex_numbers:real(complex_numbers:new(1, 2))).

'4_imaginary_part_of_a_purely_real_number_test'() ->
?assert(0 ==
complex_numbers:imaginary(complex_numbers:new(1, 0))).

'5_imaginary_part_of_a_purely_imaginary_number_test'() ->
?assert(1 ==
complex_numbers:imaginary(complex_numbers:new(0, 1))).

'6_imaginary_part_of_a_number_with_real_and_imaginary_part_test'() ->
?assert(2 ==
complex_numbers:imaginary(complex_numbers:new(1, 2))).

'7_imaginary_unit_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(-1,
0),
complex_numbers:mul(complex_numbers:new(0, 1),
complex_numbers:new(0,
1)))).

?assert(complex_numbers:equal(complex_numbers:new(3, 0),
complex_numbers:new(2,
0)))).

?assert(complex_numbers:equal(complex_numbers:new(0, 3),
complex_numbers:new(0,
2)))).

?assert(complex_numbers:equal(complex_numbers:new(4, 6),
complex_numbers:new(3,
4)))).

'11_subtract_purely_real_numbers_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(-1,
0),
complex_numbers:sub(complex_numbers:new(1, 0),
complex_numbers:new(2,
0)))).

'12_subtract_purely_imaginary_numbers_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(0,
-1),
complex_numbers:sub(complex_numbers:new(0, 1),
complex_numbers:new(0,
2)))).

'13_subtract_numbers_with_real_and_imaginary_part_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(-2,
-2),
complex_numbers:sub(complex_numbers:new(1, 2),
complex_numbers:new(3,
4)))).

'14_multiply_purely_real_numbers_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(2, 0),
complex_numbers:mul(complex_numbers:new(1, 0),
complex_numbers:new(2,
0)))).

'15_multiply_purely_imaginary_numbers_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(-2,
0),
complex_numbers:mul(complex_numbers:new(0, 1),
complex_numbers:new(0,
2)))).

'16_multiply_numbers_with_real_and_imaginary_part_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(-5,
10),
complex_numbers:mul(complex_numbers:new(1, 2),
complex_numbers:new(3,
4)))).

'17_divide_purely_real_numbers_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(5.0e-1,
0),
complex_numbers:divide(complex_numbers:new(1,
0),
complex_numbers:new(2,
0)))).

'18_divide_purely_imaginary_numbers_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(5.0e-1,
0),
complex_numbers:divide(complex_numbers:new(0,
1),
complex_numbers:new(0,
2)))).

'19_divide_numbers_with_real_and_imaginary_part_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(4.4e-1,
8.0e-2),
complex_numbers:divide(complex_numbers:new(1,
2),
complex_numbers:new(3,
4)))).

'20_absolute_value_of_a_positive_purely_real_number_test'() ->
?assert(5 ==
complex_numbers:abs(complex_numbers:new(5, 0))).

'21_absolute_value_of_a_negative_purely_real_number_test'() ->
?assert(5 ==
complex_numbers:abs(complex_numbers:new(-5, 0))).

'22_absolute_value_of_a_purely_imaginary_number_with_positive_imaginary_part_test'() ->
?assert(5 ==
complex_numbers:abs(complex_numbers:new(0, 5))).

'23_absolute_value_of_a_purely_imaginary_number_with_negative_imaginary_part_test'() ->
?assert(5 ==
complex_numbers:abs(complex_numbers:new(0, -5))).

'24_absolute_value_of_a_number_with_real_and_imaginary_part_test'() ->
?assert(5 ==
complex_numbers:abs(complex_numbers:new(3, 4))).

'25_conjugate_a_purely_real_number_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(5, 0),
complex_numbers:conjugate(complex_numbers:new(5,
0)))).

'26_conjugate_a_purely_imaginary_number_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(0,
-5),
complex_numbers:conjugate(complex_numbers:new(0,
5)))).

'27_conjugate_a_number_with_real_and_imaginary_part_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(1,
-1),
complex_numbers:conjugate(complex_numbers:new(1,
1)))).

'28_eulers_identityformula_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(-1,
0),
complex_numbers:exp(complex_numbers:new(0,
3.14159265358979311600)))).

'29_exponential_of_0_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(1, 0),
complex_numbers:exp(complex_numbers:new(0,
0)))).

'30_exponential_of_a_purely_real_number_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(2.71828182845904509080,
0),
complex_numbers:exp(complex_numbers:new(1,
0)))).

'31_exponential_of_a_number_with_real_and_imaginary_part_test'() ->
?assert(complex_numbers:equal(complex_numbers:new(-2,
0),
complex_numbers:exp(complex_numbers:new(6.93147180559945286227e-1,
3.14159265358979311600)))).``````
``````-module(complex_numbers).

-export([abs/1, add/2, conjugate/1, divide/2, equal/2, exp/1, imaginary/1, mul/2, new/2,
real/1, sub/2]).

-define(TRESHOLD, 0.005).

abs({R, I}) -> math:sqrt(math:pow(R, 2) + math:pow(I, 2)).

add({R1, I1}, {R2, I2}) -> {R1 + R2, I1 + I2}.

conjugate({R, I}) -> {R, -1 * I}.

divide({R1, I1}, {R2, I2}) ->
Divisor = math:pow(R2, 2) + math:pow(I2, 2),
{(R1 * R2 + I1 * I2) / Divisor, (I1 * R2 - R1 * I2) / Divisor}.

equal({R1, I1}, {R2, I2}) -> (erlang:abs(R1 - R2) < ?TRESHOLD) andalso (erlang:abs(I1 - I2) < ?TRESHOLD).

exp({R, I}) -> {math:exp(R) * math:cos(I), math:exp(R) * math:sin(I)}.

imaginary({_, I}) -> I.

mul({R1, I1}, {R2, I2}) -> {R1 * R2 - I1 * I2, R2 * I1 + R1 * I2}.

new(R, I) -> {R, I}.

real({R, _}) -> R.

sub({R1, I1}, {R2, I2}) -> {R1 - R2, I1 - I2}.``````