docs: function csum( arr ) {
  	if ( !Array.isArray( arr ) ) {
  		throw new TypeError( 'csum()::invalid input argument. Must provide an array.' );
  	}
  	var len = arr.length,
  		v = new Array( len );
  
  	v[ 0 ] = arr[ 0 ];
  	for ( var i = 1; i < len; i++ ) {
  		v[ i ] = v[ i-1 ] + arr[ i ];
  	}
  	return v;
  }