# evalpoly
> Evaluate a [polynomial][polynomial].
A [polynomial][polynomial] in a variable `x` can be expressed as
where `c_n, c_{n-1}, ..., c_0` are constants.
## Usage
```javascript
var evalpoly = require( '@stdlib/math/base/tools/evalpoly' );
```
#### evalpoly( c, x )
Evaluates a [polynomial][polynomial] having coefficients `c` and degree `n` at a value `x`, where `n = c.length-1`.
```javascript
var v = evalpoly( [ 3.0, 2.0, 1.0 ], 10 ); // => 3*10^0 + 2*10^1 + 1*10^2
// returns 123.0
```
The coefficients should be ordered in **ascending** degree, thus matching summation notation.
#### evalpoly.factory( c )
Uses code generation to in-line coefficients and return a `function` for evaluating a [polynomial][polynomial].
```javascript
var polyval = evalpoly.factory( [ 3.0, 2.0, 1.0 ] );
var v = polyval( 10.0 ); // => 3*10^0 + 2*10^1 + 1*10^2
// returns 123.0
v = polyval( 5.0 ); // => 3*5^0 + 2*5^1 + 1*5^2
// returns 38.0
```
## Notes
- For hot code paths in which coefficients are invariant, a compiled function will be more performant than `evalpoly()`.
- While code generation can boost performance, its use may be problematic in browser contexts enforcing a strict [content security policy][mdn-csp] (CSP). If running in or targeting an environment with a CSP, avoid using code generation.
## Examples
```javascript
var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var Float64Array = require( '@stdlib/array/float64' );
var evalpoly = require( '@stdlib/math/base/tools/evalpoly' );
var polyval;
var coef;
var sign;
var v;
var i;
// Create an array of random coefficients...
coef = new Float64Array( 10 );
for ( i = 0; i < coef.length; i++ ) {
if ( randu() < 0.5 ) {
sign = -1.0;
} else {
sign = 1.0;
}
coef[ i ] = sign * round( randu()*100.0 );
}
// Evaluate the polynomial at random values...
for ( i = 0; i < 100; i++ ) {
v = randu() * 100.0;
console.log( 'f(%d) = %d', v, evalpoly( coef, v ) );
}
// Generate an `evalpoly` function...
polyval = evalpoly.factory( coef );
for ( i = 0; i < 100; i++ ) {
v = (randu()*100.0) - 50.0;
console.log( 'f(%d) = %d', v, polyval( v ) );
}
```
[polynomial]: https://en.wikipedia.org/wiki/Polynomial
[mdn-csp]: https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP
