incrsumprod

Compute a sum of products incrementally.

The sum of products is defined as

s equals sigma-summation Underscript i equals 0 Overscript n minus 1 Endscripts x Subscript i Baseline y Subscript i

Usage

var incrsumprod = require( '@stdlib/stats/incr/sumprod' );

incrsumprod()

Returns an accumulator function which incrementally computes a sum of products.

var accumulator = incrsumprod();

accumulator( [x, y] )

If provided input values x and y, the accumulator function returns an updated sum. If not provided input value x and y, the accumulator function returns the current sum.

var accumulator = incrsumprod();

var sum = accumulator( 2.0, 3.0 );
// returns 6.0

sum = accumulator( 1.0, -1.0 );
// returns 5.0

sum = accumulator( 3.0, 4.0 );
// returns 17.0

sum = accumulator();
// returns 17.0

Notes

  • Input values are not type checked. If provided NaN or a value which, when used in computations, results in NaN, the accumulated value is NaN for all future invocations. If non-numeric inputs are possible, you are advised to type check and handle accordingly before passing the value to the accumulator function.
  • For long running accumulations or accumulations of large numbers, care should be taken to prevent overflow.

Examples

var randu = require( '@stdlib/random/base/randu' );
var incrsumprod = require( '@stdlib/stats/incr/sumprod' );

var accumulator;
var v1;
var v2;
var i;

// Initialize an accumulator:
accumulator = incrsumprod();

// For each simulated datum, update the sum-product...
for ( i = 0; i < 100; i++ ) {
    v1 = randu() * 100.0;
    v2 = randu() * 100.0;
    accumulator( v1, v2 );
}
console.log( accumulator() );