Analisis perbandingan kinerja portofolio optimal saham indeks LQ45 dengan model black-litterman pada PT Mandiri Sekuritas Tbk dan PT Bahana Securities Tbk (periode Agustus 2009-Juli 2014) = The comparative analysis of optimal portfolio performance in index shares of LQ45 with black litterman model between PT Mandiri Sekuritas Tbk and PT Bahana Securities Tbk (period of August 2009 to July 2014)