function isComplex128( dtype ) {
	return ( dtype === 'complex128' );
}
Tests whether a data type is a double-precision complex floating-point number data type.

@private
@param {string} dtype - data type
@returns {boolean} boolean indicating whether a provided data type is a double-precision complex floating-point number data type

@example
var bool = isComplex128( 'float64' );
// returns false

@example
var bool = isComplex128( 'complex128' );
// returns true