# 4.9.2. Linear Solvers

Linear solvers are defined at the sierra level. In `Solution Options` you can choose which solver to use for each activated equation.

    # Sierra > Fuego Procedure > Fuego Region
    Begin Solution Options

      USE EQUATION SOLVER muelu_cont FOR EQUATION Continuity

Note

The solver lines are optional. If you omit this line for any equation, Fuego will use a default preset solver appropriate for that transport equation.