eps2.js (1420B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 'use strict'; 20 21 // MODULES // 22 23 var ln = require( './../../../../base/special/ln' ); 24 var rateval1 = require( './rational_ak1bk1.js' ); 25 var rateval2 = require( './rational_ak2bk2.js' ); 26 var rateval3 = require( './rational_ak3bk3.js' ); 27 28 29 // MAIN // 30 31 /** 32 * Evaluates the `eps2` function. 33 * 34 * @private 35 * @param {number} eta - eta value 36 * @returns {number} function value 37 */ 38 function eps2( eta ) { 39 var lnmeta; 40 var x; 41 if ( eta < -5.0 ) { 42 x = eta * eta; 43 lnmeta = ln( -eta ); 44 return ( 12.0 - x - ( 6.0*( lnmeta*lnmeta ) ) ) / ( 12.0*x*eta ); 45 } 46 if ( eta < -2.0 ) { 47 return rateval1( eta ); 48 } 49 if ( eta < 2.0 ) { 50 return rateval2( eta ); 51 } 52 if ( eta < 1000.0 ) { 53 x = 1.0 / eta; 54 return rateval3( eta ) / ( -12.0*eta ); 55 } 56 return -1.0 / ( 12.0 * eta ); 57 } 58 59 60 // EXPORTS // 61 62 module.exports = eps2;