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 betainc = require( '@stdlib/math-base-special-betainc' );
  var isnan = require( '@stdlib/math-base-assert-is-nan' );
  var pow = require( '@stdlib/math-base-special-pow' );
  
  
  // MAIN //
  
  /**
  * Evaluates the cumulative distribution function (CDF) for a Student's t distribution with degrees of freedom `v` at a value `x`.
  *
  * @param {number} x - input value
  * @param {PositiveNumber} v - degrees of freedom
  * @returns {Probability} evaluated CDF
  *
  * @example
  * var y = cdf( 2.0, 0.1 );
  * // returns ~0.611
  *
  * @example
  * var y = cdf( 1.0, 2.0 );
  * // returns ~0.789
  *
  * @example
  * var y = cdf( -1.0, 4.0 );
  * // returns ~0.187
  *
  * @example
  * var y = cdf( NaN, 1.0 );
  * // returns NaN
  *
  * @example
  * var y = cdf( 0.0, NaN );
  * // returns NaN
  *
  * @example
  * var y = cdf( 2.0, -1.0 );
  * // returns NaN
  */
  function cdf( x, v ) {
  	var x2;
  	var p;
  	var z;
  	if (
  		isnan( x ) ||
  		isnan( v ) ||
  		v <= 0.0
  	) {
  		return NaN;
  	}
  	if ( x === 0.0 ) {
  		return 0.5;
  	}
  	x2 = pow( x, 2.0 );
  	if ( v > 2.0*x2 ) {
  		z = x2 / ( v + x2 );
  		p = betainc( z, 0.5, v/2.0, true, true ) / 2.0;
  	} else {
  		z = v / ( v + x2 );
  		p = betainc( z, v/2.0, 0.5, true, false ) / 2.0;
  	}
  	return ( x > 0.0 ) ? 1.0 - p : p;
  }
  
  
  // EXPORTS //
  
  module.exports = cdf;
  