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/**
* @license Apache-2.0
*
* Copyright (c) 2025 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 isnan = require( '@stdlib/math/base/assert/is-nan' );
var expm1 = require( '@stdlib/math/base/special/expm1' );
 
 
// MAIN //
 
/**
* Evaluates the moment-generating function (MGF) for a Planck distribution with shape parameter `lambda` at a value `t`.
*
* @param {number} t - input value
* @param {PositiveNumber} lambda - shape parameter
* @returns {number} evaluated MGF
*
* @example
* var y = mgf( 0.2, 0.5 );
* // returns ~1.5181
*
* @example
* var y = mgf( 0.4, 1.5 );
* // returns ~1.1645
*
* @example
* var y = mgf( NaN, 0.0 );
* // returns NaN
*
* @example
* var y = mgf( 0.0, NaN );
* // returns NaN
*
* @example
* var y = mgf( 2.0, -1.0 );
* // returns NaN
*/
function mgf( t, lambda ) {
	if ( isnan( t ) || isnan( lambda ) || lambda <= 0.0 ) {
		return NaN;
	}
	return expm1( -lambda ) / expm1( t - lambda );
}
 
 
// EXPORTS //
 
module.exports = mgf;