:<math> \begin{align} & \mathbf{J^{(0)}(r)} = (1+\alpha) \mathbf{ \hat{n} \times H^{inc}(r) } \\ & \mathbf{M^{(0)}(r)} = -(1-\alpha) \mathbf{ \hat{n} \times E^{inc}(r) } \end{align} </math>
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:<math> \mathbf{J^{(0)}(r)} = \mathbf{\hat{n}\times} \begin{bmatrix} 1-R_{||} & 0 \\ 0 & 1-R_{\perp} \end{bmatrix} \cdot \begin{bmatrix} \mathbf{H_{||}^{inc}(r)} \\ \mathbf{H_{\perp}^{inc}(r)} \end{bmatrix} </math>
:<math> \mathbf{M^{(0)}(r)} = -\mathbf{\hat{n}\times} \begin{bmatrix} 1+R_{||} & 0 \\ 0 & 1+R_{\perp} \end{bmatrix} \cdot \begin{bmatrix} \mathbf{E_{||}^{inc}(r)} \\ \mathbf{E_{\perp}^{inc}(r)} \end{bmatrix} </math>
which are the conventional PO currents. However, this approximation does not formally recognize the lit and shadowed areas. Instead of identifying the exact boundaries of the lit and shadowed areas over a complex target, a simple condition is used first to find the primary shadowed areas. Then, through PO iterations all shadowed areas are determined automatically. When calculating the field on the scatterer for every source point, a primary shadowing condition given by '''n.k'''< 0 is examined. In complex scatterer geometries, there are shadowed points in concave regions where '''n.k'''> 0, but the correct shadowing is eventually achieved through the iteration of the PO currents. Therefore, in computation of the above equations, only the contribution of the points that satisfy the following condition are considered: