compute-polynomial

Evaluates a polynomial.

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compute-polynomial
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polynomial
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Evaluates a polynomial.

Installation

``\$ npm install compute-polynomial``

For use in the browser, use browserify.

Usage

``var polyval = require( 'compute-polynomial' );``

polyval( coef, x, options )

Evaluates a polynomial whose coefficients are defined by `coef`. `x` may be either a single `numeric` value or an `array` of values at which to evaluate to the polynomial.
The coefficients should be ordered in descending degree. For example, for a polynomial
``a_nx^n + a_(n-1)x^(n-1) + ... + a_1x^1 + a_0x^0``

the coefficients would be
``[a_n, a_(n-1),..., a_1, a_0]``

Consider the polynomial `4x^3 + 2x^2 + 6x - 17`. To evaluate the polynomial at a single value,
``````var val = polyval( [ 4, 2, 6, -17 ], 10 );
// returns 4243``````

To evaluate the polynomial at multiple values,
``````var vals = polyval( [ 4, 2, 6, -17 ], [ 10, -3 ] );
// returns [ 4243, -125 ]``````

When provided an input `array`, the function accepts the following `options`:
• copy: `boolean` indicating whether to return a new `array`. Default: `true`.
• accessor: accessor `function` for accessing numeric values in object `arrays`.

To mutate the input `array` (e.g., when input values can be discarded or when optimizing memory usage), set the `copy` option to `false`.
``````var coefs = [ 4, 2, 6, -17 ],
x = [ 10, -3 ];

var vals = polyval( coefs, x, {
'copy': false
});
// returns [ 4243, -125 ]

console.log( x === vals );
// returns true``````

For object `arrays`, provide an accessor `function` for accessing `array` values.
``````var coefs = [ 4, 2, 6, -17 ];

var data = [
['beep', 10],
['boop', -3]
];

function getValue( d, i ) {
return d[ 1 ];
}

var vals = polyval( coefs, data, {
'accessor': getValue
});
// returns [ 4243, -125 ]``````

Examples

``````var polyval = require( 'compute-polynomial' );

var coef = new Array( 25 ),
sign;

for ( var i = 0; i < coef.length; i++ ) {
sign = 1;
if ( Math.random()-0.5 < 0 ) {
sign = -1;
}
coef[ i ] = sign * Math.round( Math.random()*i );
}

// Evaluate the polynomial at a single value:
console.log( polyval( coef, 10 ) );

// Evaluate the polynomial at multiple values:
console.log( polyval( coef, [ 10, -10 ] ) );``````

To run the example code from the top-level application directory,
``\$ node ./examples/index.js``

Notes

This method implements Horner's rule to achieve efficient computation.

Tests

Unit

Unit tests use the Mocha test framework with Chai assertions. 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``