TeX source:

\rho'_{AB|+} = \dfrac{(\mathbf{M}_{+A}\otimes\mathbf{I}_B)\rho_{AB}(\mathbf{M}_{+A}\otimes\mathbf{I}_B)}{\text{tr}\{(\mathbf{M}_{+A}\otimes\mathbf{I}_B)\rho_{AB}\}}.