toArray( array = [], offset = 0 ) {

		const coefficients = this.coefficients;

		for ( let i = 0; i < 9; i ++ ) {

			coefficients[ i ].toArray( array, offset + ( i * 3 ) );

		}

		return array;

	}
Returns an array with the SH coefficients, or copies them into the provided
array. The coefficients are represented as numbers.

@param {Array<number>} [array=[]] - The target array.
@param {number} [offset=0] - The array offset where to start copying.
@return {Array<number>} An array with flat SH coefficients.