time-to-botec

README.md (5893B)

---

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 # gammainc
 
 > [Incomplete gamma function][incomplete-gamma-function].
 
 <section class="intro">
 
 Evaluates the regularized lower [incomplete gamma function][incomplete-gamma-function]:
 
 <!-- <equation class="equation" label="eq:lower_incomplete_gamma" align="center" raw="P( x, a ) = \frac{\gamma(a,x)}{\Gamma(a)} = \frac{1}{\Gamma(a)} \int_0^x t^{a-1} e^{-t} \; dt" alt="Regularized lower incomplete gamma function."> -->
 
 <div class="equation" align="center" data-raw-text="P( x, a ) = \frac{\gamma(a,x)}{\Gamma(a)} = \frac{1}{\Gamma(a)} \int_0^x t^{a-1} e^{-t} \; dt" data-equation="eq:lower_incomplete_gamma">
     <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@bb29798906e119fcb2af99e94b60407a270c9b32/lib/node_modules/@stdlib/math/base/special/gammainc/docs/img/equation_lower_incomplete_gamma.svg" alt="Regularized lower incomplete gamma function.">
     <br>
 </div>
 
 <!-- </equation> -->
 
 The function can also be used to evaluate the regularized upper incomplete gamma function, which is defined as follows:
 
 <!-- <equation class="equation" label="eq:upper_incomplete_gamma" align="center" raw="Q( x, a ) = \frac{\Gamma(a,x)}{\Gamma(a)} = \frac{1}{\Gamma(a)} \int_x^\infty t^{a-1} e^{-t} \; dt" alt="Regularized upper incomplete gamma function."> -->
 
 <div class="equation" align="center" data-raw-text="Q( x, a ) = \frac{\Gamma(a,x)}{\Gamma(a)} = \frac{1}{\Gamma(a)} \int_x^\infty t^{a-1} e^{-t} \; dt" data-equation="eq:upper_incomplete_gamma">
     <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@bb29798906e119fcb2af99e94b60407a270c9b32/lib/node_modules/@stdlib/math/base/special/gammainc/docs/img/equation_upper_incomplete_gamma.svg" alt="Regularized upper incomplete gamma function.">
     <br>
 </div>
 
 <!-- </equation> -->
 
 The two functions have the relationship `Q(x,a) = 1 - P(x,a)`.
 
 In addition, this routine can be used to evaluate the _unregularized_ gamma functions. The range of above functions is `[0,1]`, which is not the case for the _unregularized_ versions. The unregularized lower incomplete gamma function is defined as
 
 <!-- <equation class="equation" label="eq:unreg_lower_incomplete_gamma" align="center" raw="\gamma(a,x) = \int_0^x t^{a-1} e^{-t} \; dt" alt="Unregularized lower incomplete gamma function."> -->
 
 <div class="equation" align="center" data-raw-text="\gamma(a,x) = \int_0^x t^{a-1} e^{-t} \; dt" data-equation="eq:unreg_lower_incomplete_gamma">
     <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@bb29798906e119fcb2af99e94b60407a270c9b32/lib/node_modules/@stdlib/math/base/special/gammainc/docs/img/equation_unreg_lower_incomplete_gamma.svg" alt="Unregularized lower incomplete gamma function.">
     <br>
 </div>
 
 <!-- </equation> -->
 
 and the upper unregularized incomplete gamma function is
 
 <!-- <equation class="equation" label="eq:unreg_upper_incomplete_gamma" align="center" raw="\Gamma(a,x)= \int_x^\infty t^{a-1} e^{-t} \; dt" alt="Unregularized upper incomplete gamma function."> -->
 
 <div class="equation" align="center" data-raw-text="\Gamma(a,x)= \int_x^\infty t^{a-1} e^{-t} \; dt" data-equation="eq:unreg_upper_incomplete_gamma">
     <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@bb29798906e119fcb2af99e94b60407a270c9b32/lib/node_modules/@stdlib/math/base/special/gammainc/docs/img/equation_unreg_upper_incomplete_gamma.svg" alt="Unregularized upper incomplete gamma function.">
     <br>
 </div>
 
 <!-- </equation> -->
 
 The relationship between the two functions is `Γ(a,x) = γ(a,x) + Γ(a)`.
 
 </section>
 
 <!-- /.intro -->
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var gammainc = require( '@stdlib/math/base/special/gammainc' );
 ```
 
 #### gammainc( x, s\[, regularized\[, upper ]] )
 
 By default, evaluates the regularized lower [incomplete gamma function][incomplete-gamma-function] for inputs `x` and `s`. The third and fourth parameters of the function can be used to specify whether instead to evaluate the non-regularized and/or upper incomplete gamma functions, respectively.
 
 ```javascript
 var y = gammainc( 6.0, 2.0 );
 // returns ~0.9826
 
 y = gammainc( 1.0, 2.0, true, true );
 // returns ~0.7358
 
 y = gammainc( 7.0, 5.0 );
 // returns ~0.8270
 
 y = gammainc( 7.0, 5.0, false );
 // returns ~19.8482
 ```
 
 If provided `NaN` as any argument, the function returns `NaN`.
 
 ```javascript
 var y = gammainc( NaN, 1.0 );
 // returns NaN
 
 y = gammainc( 1.0, NaN );
 // returns NaN
 ```
 
 If provided a negative `x`, the function returns `NaN`.
 
 ```javascript
 var y = gammainc( -2.0, 2.0 );
 // returns NaN
 ```
 
 If provided a nonpositive `s`, the function returns `NaN`.
 
 ```javascript
 var y = gammainc( 2.0, -1.0 );
 // returns NaN
 
 y = gammainc( 2.0, 0.0 );
 // returns NaN
 ```
 
 </section>
 
 <!-- /.usage -->
 
 <section class="examples">
 
 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var randu = require( '@stdlib/random/base/randu' );
 var gammainc = require( '@stdlib/math/base/special/gammainc' );
 
 var i;
 var x;
 var s;
 
 for ( i = 0; i < 100; i++ ) {
     x = randu() * 10.0;
     s = randu() * 10.0;
     console.log( 'x: %d, \t s: %d, \t f(x,s): %d', x.toFixed( 4 ), s.toFixed( 4 ), gammainc( x, s ).toFixed( 4 ) );
 }
 ```
 
 </section>
 
 <!-- /.examples -->
 
 <section class="links">
 
 [incomplete-gamma-function]: https://en.wikipedia.org/wiki/Incomplete_gamma_function
 
 </section>
 
 <!-- /.links -->