math-evalpoly

evalpoly

Evaluates a polynomial.

Installation

$ npm install math-evalpoly

Usage

var evalpoly = require( 'math-evalpoly' );

evalpoly( c, x )

Evaluates a polynomial having coefficients c and degree n at a value x, where n = c.length-1.

var v = evalpoly( [3,2,1], 10 );
// returns 123 => 3*10^0 + 2*10^1 + 1*10^2

The coefficients should be ordered in ascending degree. For example, for a polynomial

the coefficients would be

[c_0, c_1, ..., c_(n-1), c_n]

matching the summation notation.

evalpoly.factory( c )

Uses code generation to in-line coefficients and return a reusable function for evaluating a polynomial.

var poly = evalpoly.factory( [3,2,1] );

var v = poly( 10 );
// returns 123 => 3*10^0 + 2*10^1 + 1*10^2

v = poly( 5 );
// returns 38 => 3*5^0 + 2*5^1 + 1*5^2

Note: For hot code paths in which coefficients are invariant, the generated function will be more performant than the main export.

Examples

var round = require( 'math-round' );
var evalpoly = require( 'math-evalpoly' );

var coef;
var sign;
var poly;
var v;
var i;

// Create an array of random coefficients...
coef = new Float64Array( 10 );
for ( i = 0; i < coef.length; i++ ) {
	if ( Math.random() < 0.5 ) {
		sign = -1;
	} else {
		sign = 1;
	}
	coef[ i ] = sign * round( Math.random()*100 );
}

// Evaluate the polynomial at random values...
for ( i = 0; i < 100; i++ ) {
	v = Math.random() * 100;
	console.log( 'f(%d) = %d', v, evalpoly( coef, v ) );
}

// Generate an `evalpoly` function...
poly = evalpoly.factory( coef );
for ( i = 0; i < 100; i++ ) {
	v = Math.random()*100 - 50;
	console.log( 'f(%d) = %d', v, poly( v ) );
}

To run the example code from the top-level application directory,

$ node ./examples/index.js

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Tests

Unit

This repository uses tape for unit tests. To run the tests, execute the following command in the top-level application directory:

$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

$ make view-cov

Browser Support

This repository uses Testling for browser testing. To run the tests in a (headless) local web browser, execute the following command in the top-level application directory:

$ make test-browsers

To view the tests in a local web browser,

$ make view-browser-tests

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License

MIT license.

Copyright

Copyright © 2016. The Compute.io Authors..