text: /**
  * @license Apache-2.0
  *
  * Copyright (c) 2018 The Stdlib Authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *    http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
  
  'use strict';
  
  // MODULES //
  
  var digamma = require( '@stdlib/math-base-special-digamma' );
  var betaln = require( '@stdlib/math-base-special-betaln' );
  
  
  // MAIN //
  
  /**
  * Returns the differential entropy of a beta distribution.
  *
  * @param {PositiveNumber} alpha - first shape parameter
  * @param {PositiveNumber} beta - second shape parameter
  * @returns {NonPositiveNumber} differential entropy
  *
  * @example
  * var v = entropy( 1.0, 1.0 );
  * // returns 0.0
  *
  * @example
  * var v = entropy( 4.0, 12.0 );
  * // returns ~-0.869
  *
  * @example
  * var v = entropy( 8.0, 2.0 );
  * // returns ~-0.795
  *
  * @example
  * var v = entropy( 1.0, -0.1 );
  * // returns NaN
  *
  * @example
  * var v = entropy( -0.1, 1.0 );
  * // returns NaN
  *
  * @example
  * var v = entropy( 2.0, NaN );
  * // returns NaN
  *
  * @example
  * var v = entropy( NaN, 2.0 );
  * // returns NaN
  */
  function entropy( alpha, beta ) {
  	var out;
  	if ( alpha <= 0.0 || beta <= 0.0 ) {
  		return NaN;
  	}
  	out = betaln( alpha, beta );
  	out -= ( alpha-1.0 ) * digamma( alpha );
  	out -= ( beta-1.0 ) * digamma( beta );
  	out += ( alpha+beta-2.0 ) * digamma( alpha+beta );
  	return out;
  }
  
  
  // EXPORTS //
  
  module.exports = entropy;
  