# 4.9. Solution Options

The `Solution Options` block in the Fuego region is where you define what equations to solve, sub-models to use, and nonlinear and linear solver configurations. The most commonly used commands in this block are:

> - What equations you want to solve

> - What linear solver to use for each equation

> - The problem coordinate system

> - Source terms for your equations

> - What smoothing method to use for the pressure solve

> - What advection methods to use for each transport equation

> - Nonlinear iteration settings (tolerances and iteration counts)

> - EDC combustion model parameters

> - Turbulence model specifications

> - Buoyancy model specifications

    # Sierra > Fuego Procedure > Fuego Region
    # Non-isothermal 2D ksgs example solution options
    Begin Solution Options
      Coordinate System = 2D
      Projection Method = Fourth_Order Smoothing with Timestep Scaling

      # DEFINE WHAT EQUATIONS TO SOLVE
      Activate Equation Enthalpy

      # DEFINE NONLINEAR ITERATION SETTINGS
      Minimum Number of Nonlinear Iterations = 1
      Maximum Number of Nonlinear Iterations = 2

      # DEFINE ADVECTION SCHEME
      Upwind Method is MUSCL
      UPWIND LIMITER IS SuperBee

      Begin Turbulence Model Specification
        Turbulence Model = KSGS
      End

    End   Solution Options

The most common commands are described in the sections below, and the complete list of available commands for the solution options block and the syntax for the different options can be found in Solution Control Description.

- 4.9.1. Equations To Solve
- 4.9.2. Linear Solvers
- 4.9.3. Coordinate System
- 4.9.4. Source terms
  - 4.9.4.1. External Sources
  - 4.9.4.2. Subroutines and String Functions
  - 4.9.4.3. Point Sources
- 4.9.5. Smoothing Method
- 4.9.6. Advection Methods
  - 4.9.6.1. Central Difference
  - 4.9.6.2. Upwind Method
  - 4.9.6.3. MUSCL Upwind
  - 4.9.6.4. Fuego Blending Approach
- 4.9.7. Nonlinear Iteration Settings
- 4.9.8. Turbulence Model
- 4.9.9. Buoyancy Model