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# NEWTON_SOLVER¶

Specifies nonlinear solver parameters associated with convergence and Jacobian matrix format

## Required Cards:¶

- NEWTON_SOLVER <string>
- Specifies nonlinear solver for flow or transport (i.e. FLOW or TRANSPORT).

## Optional Cards:¶

- NO_INFINITY_NORM
- Toggle off calculation of infinity norm on residual and update vectors. The default is to calculate infinity norm.
- NO_FORCE_ITERATION
- Toggle off the forcing of at least 1 linear iteration. The default is to force at least 1 linear iteration. In a quasi-stationary state, the initial residual may be sufficiently small for convergence, but sometimes it is better to force at least one iteration.
- NO_PRINT_CONVERGENCE
- Toggle off printing of convergence information.
- PRINT_DETAILED_CONVERGENCE
- Toggle on printing of detailed convergence information. Warning: this can be a lot of information to parse.

**Note: See the** PETSc **users manual for a more definitive explanation of the solver atol, rtol, and stol tolerances below.**

- ATOL <float>
- Absolute tolerance. Absolute size of 2-norm of residual, i.e.
- ||f(x_n)|| < ATOL

- RTOL <float>
- Relative tolerance. Relative decrease in size of 2-norm of residual, i.e.
- ||f(x_n)||/||f(x_0)|| < RTOL

- STOL <float>
- Relative update tolerance. Relative decrease in size of 2-norm of solution, i.e.
- ||x_n-x_(n-1)||/||x_(n-1)-x_(n-2)|| < STOL

- ITOL <float>
- Infinity tolerance. Size of infinity norm of residual, i.e.
- ||f(x_n)||_inf < ITOL

- ITOL_UPDATE <float>
- Infinity tolerance. Size of infinity norm of update, i.e.
- ||x_n-x_(n-1)||_inf < ITOL_UPDATE

- MAXIT <int>
- Maximum number of Newton iterations before reporting failed convergence.
- MAXF <int>
- Maximum number of function evaluations before reporting failed convergence.
- MATRIX_TYPE <string>
- Format of main solver matrix. PETSc Mat (i.e. AIJ, BAIJ, or HYPRESTRUCT).
- PRECONDITIONER_MATRIX_TYPE <string >
- Format of preconditioning matrix. PETSc Mat (i.e. AIJ, BAIJ, or HYPRESTRUCT). Default is same as solver.

## Examples¶

NEWTON_SOLVER FLOW ITOL_UPDATE 1.d0 / NEWTON_SOLVER FLOW PRECONDITIONER_MATRIX_TYPE AIJ RTOL 1.d-8 ATOL 1.d-8 STOL 1.d-30 ITOL_UPDATE 1.d0 / NEWTON_SOLVER TRANSPORT PRECONDITIONER_MATRIX_TYPE AIJ RTOL 1.d-12 ATOL 1.d-12 STOL 1.d-30 MAXIT 10 NO_INFINITY_NORM NO_PRINT_CONVERGENCE /