# incrmsumabs2

Compute a moving sum of squared absolute values incrementally.

For a window of size W, the moving sum of squared absolute values is defined as

## Usage

var incrmsumabs2 = require( '@stdlib/stats/incr/msumabs2' );


#### incrmsumabs2( window )

Returns an accumulator function which incrementally computes a moving sum of squared absolute values. The window parameter defines the number of values over which to compute the moving sum.

var accumulator = incrmsumabs2( 3 );


#### accumulator( [x] )

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

var accumulator = incrmsumabs2( 3 );

var sum = accumulator();
// returns null

// Fill the window...
sum = accumulator( 2.0 ); // [2.0]
// returns 4.0

sum = accumulator( -1.0 ); // [2.0, -1.0]
// returns 5.0

sum = accumulator( 3.0 ); // [2.0, -1.0, 3.0]
// returns 14.0

// Window begins sliding...
sum = accumulator( -7.0 ); // [-1.0, 3.0, -7.0]
// returns 59.0

sum = accumulator( -5.0 ); // [3.0, -7.0, -5.0]
// returns 83.0

sum = accumulator();
// returns 83.0

• 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 at least W-1 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.
• As W values are needed to fill the window buffer, the first W-1 returned values are calculated from smaller sample sizes. Until the window is full, each returned value is calculated from all provided values.