Iterative Weight Constraints for a Multi-Asset Portfolio

Summary

The document explains why a portfolio weight constraint routine can fail when it caps bond exposure and then normalizes all weights. Normalization may push the bond allocation above its intended limit; the example describes a bond weight of 20% becoming 40% when the total portfolio weights sum to 50%. This makes the order of constraint operations important.

It proposes an iterative method that normalizes initial weights, applies per-asset floors and ceilings, and redistributes remaining weight among unconstrained assets until the portfolio sums to one and respects the bounds. It also checks for infeasible floor and cap combinations. The document provides code but no test results or evidence that the proposed routine converges for every input. Its practical use depends on feasible bounds and on verifying that the iteration reaches a valid solution within its iteration limit.

Key ideas

• Capping bond exposure before normalizing can allow normalization to breach the bond limit.
• Redistributing weight among assets that are not at their bounds can preserve a total allocation of one.
• The proposed routine enforces per-asset floors and ceilings through repeated adjustment.
• The floor and cap settings must be feasible for the number of assets and their total allocation.

Tags

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.