public final void postmultiply(Matrix matrix) {
		for (int i = 0; i < 4; i++)
			for (int j = 0; j < 4; j++) {
				entry2[i][j] = 0.0;
				for (int k = 0; k < 4; k++)
					entry2[i][j] += entry[i][k] * matrix.entry[k][j];
			}
		// Swap!
		double[][] oldentry = entry;
		entry = entry2;
		entry2 = oldentry;
	}