  A solid object's geometry, density, and elastic moduli completely determine
its spectrum of normal modes. Solving the inverse problem - determining a
material's elastic moduli given a set of resonance frequencies and sample
geometry - relies on the ability to compute resonance spectra accurately and
efficiently. Established methods for calculating these spectra are either fast
but limited to simple geometries, or are applicable to arbitrarily shaped
samples at the cost of being prohibitively slow. Here, we describe a method to
rapidly compute the normal modes of irregularly shaped objects using entirely
open-source software. Our method's accuracy compares favorably with existing
methods for simple geometries and shows a significant improvement in speed over
existing methods for irregular geometries.
