  Heliophysics theory and modeling build understanding from fundamental
principles to motivate, interpret, and predict observations. Together with
observational analysis, they constitute a comprehensive scientific program in
heliophysics. As observations and data analysis become increasingly detailed,
it is critical that theory and modeling develop more quantitative predictions
and iterate with observations. Advanced theory and modeling can inspire and
greatly improve the design of new instruments and increase their chance of
success. In addition, in order to build physics-based space weather forecast
models, it is important to keep developing and testing new theories, and
maintaining constant communications with theory and modeling. Maintaining a
sustainable effort in theory and modeling is critically important to
heliophysics. We recommend that all funding agencies join forces and consider
expanding current and creating new theory and modeling programs--especially, 1.
NASA should restore the HTMS program to its original support level to meet the
critical needs of heliophysics science; 2. a Strategic Research Model program
needs to be created to support model development for next-generation basic
research codes; 3. new programs must be created for addressing mission-critical
theory and modeling needs; and 4. enhanced programs are urgently required for
training the next generation of theorists and modelers.

Instrumentation and Methods for Astrophysics;Solar and Stellar Astrophysics;Plasma Physics;Space Physics