Resumen
We propose a fully polynomial bicriteria approximation scheme for the constrained spanning tree problem. First, an exact pseudo-polynomial algorithm is developed based on a two-variable extension of the well-known matrix-tree theorem. The scaling and approximate binary search techniques are then utilized to yield a fully polynomial approximation scheme.

Resumen
We consider the deadline problem and budget problem of the nonlinear time–cost tradeoff project scheduling model in a series–parallel activity network. We develop fully polynomial-time approximation schemes for both problems using K-approximation sets and functions, together with series and parallel reductions.