Non-modal melting কী?

In non-modal melting, the minerals of the source enter the melt in proportions $p_i$ that differ from their mass fractions $x_i$ in the source. The melt then sees the bulk partition coefficient of the source, $D_0 = \sum_i x_iD_i$, at the start and the melting-weighted coefficient $P = \sum_i p_iD_i$ as it grows.