SMARTPHONE PURCHASING DECISION MAKING USING AN INTERVAL-VALUED INTUITIONISTIC FUZZY AHP APPROACH: A CASE STUDY IN MALANG CITY - Hidayat, Noor; Krisnawati, Vira Hari; Abusini, Sobri; Khairi, Desfi Rahmatul (BAREKENG: Jurnal Ilmu Matematika dan Terapan, 2026)