Analisis pengaruh rasio keuangan terhadap profitabilitas bank syariah (studi kasus pada Bank Pembiayaan Rakyat Syariah di Indonesia Periode Triwulan II 2011 - Triwulan IV 2012) = analysis on the impact of financial ratio towards islamic bank profitability (Case Study On Islamic Rural Banks In Indonesia 2011Q2 - 2012Q4)