1 : import { FuzzySet } from '../FuzzySet.js';
2 : 
3 : /**
4 : * Class for representing a fuzzy set that has a normal distribution shape. It can be defined
5 : * by the mean and standard deviation.
6 : *
7 : * @author {@link https://github.com/robp94|robp94}
8 : * @augments FuzzySet
9 : */
10 : class NormalDistFuzzySet extends FuzzySet {
11 : 
12 : 	/**
13 : 	* Constructs a new triangular fuzzy set with the given values.
14 : 	*
15 : 	* @param {Number} left - Represents the left border of this fuzzy set.
16 : 	* @param {Number} midpoint - Mean or expectation of the normal distribution.
17 : 	* @param {Number} right - Represents the right border of this fuzzy set.
18 : 	* @param {Number} standardDeviation - Standard deviation of the normal distribution.
19 : 	*/
20 : 	constructor( left = 0, midpoint = 0, right = 0, standardDeviation = 0 ) {
21 : 
22 : 		super( midpoint );
23 : 
24 : 		/**
25 : 		* Represents the left border of this fuzzy set.
26 : 		* @type {Number}
27 : 		* @default 0
28 : 		*/
29 : 		this.left = left;
30 : 
31 : 		/**
32 : 		* Represents the peak value of this fuzzy set.
33 : 		* @type {Number}
34 : 		* @default 0
35 : 		*/
36 : 		this.midpoint = midpoint;
37 : 
38 : 		/**
39 : 		* Represents the right border of this fuzzy set.
40 : 		* @type {Number}
41 : 		* @default 0
42 : 		*/
43 : 		this.right = right;
44 : 
45 : 		/**
46 : 		* Represents the standard deviation of this fuzzy set.
47 : 		* @type {Number}
48 : 		* @default 0
49 : 		*/
50 : 		this.standardDeviation = standardDeviation;
51 : 
52 : 		//
53 : 
54 : 		this._cache = {};
55 : 
56 : 	}
57 : 
58 : 	/**
59 : 	* Computes the degree of membership for the given value.
60 : 	*
61 : 	* @param {Number} value - The value used to calculate the degree of membership.
62 : 	* @return {Number} The degree of membership.
63 : 	*/
64 : 	computeDegreeOfMembership( value ) {
65 : 
66 : 		this._updateCache();
67 : 
68 : 		if ( value >= this.right || value <= this.left ) return 0;
69 : 
70 : 		return probabilityDensity( value, this.midpoint, this._cache.variance ) / this._cache.normalizationFactor;
71 : 
72 : 	}
73 : 
74 : 	/**
75 : 	* Transforms this instance into a JSON object.
76 : 	*
77 : 	* @return {Object} The JSON object.
78 : 	*/
79 : 	toJSON() {
80 : 
81 : 		const json = super.toJSON();
82 : 
83 : 		json.midpoint = this.midpoint;
84 : 		json.standardDeviation = this.standardDeviation;
85 : 
86 : 		return json;
87 : 
88 : 	}
89 : 
90 : 	/**
91 : 	* Restores this instance from the given JSON object.
92 : 	*
93 : 	* @param {Object} json - The JSON object.
94 : 	* @return {NormalDistFuzzySet} A reference to this fuzzy set.
95 : 	*/
96 : 	fromJSON( json ) {
97 : 
98 : 		super.fromJSON( json );
99 : 
100 : 		this.midpoint = json.midpoint;
101 : 		this.standardDeviation = json.standardDeviation;
102 : 
103 : 		return this;
104 : 
105 : 	}
106 : 
107 : 	//
108 : 
109 : 	_updateCache() {
110 : 
111 : 		const cache =	this._cache;
112 : 		const midpoint = this.midpoint;
113 : 		const standardDeviation = this.standardDeviation;
114 : 
115 : 		if ( midpoint !== cache.midpoint || standardDeviation !== cache.standardDeviation ) {
116 : 
117 : 			const variance = standardDeviation * standardDeviation;
118 : 
119 : 			cache.midpoint = midpoint;
120 : 			cache.standardDeviation = standardDeviation;
121 : 			cache.variance = variance;
122 : 
123 : 			// this value is used to ensure the DOM lies in the range of [0,1]
124 : 
125 : 			cache.normalizationFactor = probabilityDensity( midpoint, midpoint, variance );
126 : 
127 : 		}
128 : 
129 : 		return this;
130 : 
131 : 	}
132 : 
133 : }
134 : 
135 : //
136 : 
137 : function probabilityDensity( x, mean, variance ) {
138 : 
139 : 	return ( 1 / Math.sqrt( 2 * Math.PI * variance ) ) * Math.exp( - ( Math.pow( ( x - mean ), 2 ) ) / ( 2 * variance ) );
140 : 
141 : }
142 : 
143 : export { NormalDistFuzzySet };