GMS:NWT Package: Difference between revisions
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{{MODFLOW Links}} | {{MODFLOW Links}} | ||
[[File:NWTsolver.jpg|thumb|500 px|Example of the ''MODFLOW NWT Solver'' dialog.]] | [[File:NWTsolver.jpg|thumb|500 px|Example of the ''MODFLOW NWT Solver'' dialog.]] | ||
The Newton package (NWT) is one of the solvers available in MODFLOW-NWT. The NWT package is only used with the [[GMS:UPW Package|UPW Package]]. Using the NWT solver requires twice the memory of other MODFLOW solvers because using the Newton method results in an asymmetric matrix. Because of the asymmetric matrix a different matrix solver must be used. The NWT package provides an option to use one of two matrix solvers: a generalized-minimum-residual (GMRES) solver and an Orthomin/stabilized conjugate-gradient solver called χMD (chi-MD). | The Newton package (NWT) is one of the solvers available in MODFLOW-NWT. The NWT package is only used with the [[GMS:UPW Package|UPW Package]]. Using the NWT solver requires twice the memory of other MODFLOW solvers because using the Newton method results in an asymmetric matrix. Because of the asymmetric matrix a different matrix solver must be used. The NWT package provides an option to use one of two matrix solvers: a generalized-minimum-residual (GMRES) solver and an Orthomin/stabilized conjugate-gradient solver called χMD (chi-MD). | ||
==General Options== | ==General Options== | ||
*Comments (Text) – Allows up to 199 characters. | *''Comments (Text)'' – Allows up to 199 characters. | ||
*Max head change between outer iterations (L)(HEADTOL) | *''Max head change between outer iterations (L)(HEADTOL)'' – For solution of the nonlinear problem. | ||
*Max root-mean-squared flux difference between outer iterations (L^3/T) (FLUXTOL) | *''Max root-mean-squared flux difference between outer iterations (L^3/T) (FLUXTOL)'' – For solution of the nonlinear problem. | ||
*Max number of iterations allowed for outer problem (MAXITEROUT) | *''Max number of iterations allowed for outer problem (MAXITEROUT)'' – For solution of the nonlinear problem. | ||
*Portion of cell thickness used for adjusting coefficients to zero (THICKFACT) | *''Portion of cell thickness used for adjusting coefficients to zero (THICKFACT)'' – The portion of the cell thickness (length) used for smoothly adjusting storage and conductance coefficients to zero. | ||
*Matrix solver to be used (LINMETH) – A flag that determines which matrix solver will be used. | *''Matrix solver to be used (LINMETH)'' – A flag that determines which matrix solver will be used. | ||
<blockquote style="margin-top:0px; margin-bottom:0px;"> | |||
* (1) GMRES | |||
*Print additional info to listing file (IPRNWT) | * (2) χMD | ||
*Correct head relative to cell-bottom if surrounded by | </blockquote> | ||
*Options (OPTIONS) – Includes | *''Print additional info to listing file (IPRNWT)'' – A flag that indicates whether additional information about solver convergence will be printed to the main listing file | ||
*''Correct head relative to cell-bottom if surrounded by dewatered cells (IBOTAV)'' – A flag that indicates whether corrections will be made to groundwater head relative to the cell-bottom altitude if the cell is surrounded by dewatered cells. | |||
<blockquote style="margin-top:0px; margin-bottom:0px;"> | |||
* (0) Don't correct | |||
* (1) Correct | |||
</blockquote> | |||
*''Options (OPTIONS)'' – Includes the following options: | |||
<blockquote style="margin-top:0px; margin-bottom:0px;"> | |||
* SPECIFIED – Indicates that the optional solver input values will be entered by the user. | |||
* SIMPLE – Indicates that default solver input values will be defined that work well for nearly linear models. | |||
* MODERATE – Indicates that default solver input values will be defined that work well for moderately nonlinear models. | |||
* COMPLEX – Indicates that default solver input values will be defined that work well for highly nonlinear models. | |||
<!--* CONTINUE – Without this the model will stop after convergence failure.--> | |||
</blockquote> | |||
==General Specified Options== | ==General Specified Options== | ||
*Coefficient to reduce weight applied to head change (DBDTHETA) – Used to control oscillations in head. Values range between 0.0 and 1.0, and larger values increase the weight (decrease under-relaxation) applied to the head change. | *''Coefficient to reduce weight applied to head change (DBDTHETA)'' – Used to control oscillations in head. Values range between 0.0 and 1.0, and larger values increase the weight (decrease under-relaxation) applied to the head change. | ||
*Coefficient to increase weight applied to head change (DBDKAPPA) – Used to control oscillations in head. Values range between 0.0 and 1.0, and larger values increase the weight applied to the head change. | *''Coefficient to increase weight applied to head change (DBDKAPPA)'' – Used to control oscillations in head. Values range between 0.0 and 1.0, and larger values increase the weight applied to the head change. | ||
*Factor used to weight the head change for iterations n&ndashl1 and n (DBGGAMMA) – Values range between 0.0 and 1.0, and greater values apply more weight to the head change calculated during iteration ''n''. | *''Factor used to weight the head change for iterations n&ndashl1 and n (DBGGAMMA)'' – Values range between 0.0 and 1.0, and greater values apply more weight to the head change calculated during iteration ''n''. | ||
*Momentum coefficient (MOMFACT) – Ranges between 0.0 and 1.0. Greater values apply more weight to the head change for iteration ''n''. | *''Momentum coefficient (MOMFACT)'' – Ranges between 0.0 and 1.0. Greater values apply more weight to the head change for iteration ''n''. | ||
*Use residual control (BACKFLAG) – Specify whether residual control will be used. | *''Use residual control (BACKFLAG)'' – Specify whether residual control will be used. | ||
<blockquote style="margin-top:0px; margin-bottom:0px;"> | |||
* 1 = active | |||
*Max number of reductions (backtracks) in head change (MAXBACKITER) – A value between 10 and 50 works well. Only read if residual control is active. | * 0 = inactive | ||
*Proportional decrease in root-mean-squared error (BACKTOL) – Only read if residual control is active. | </blockquote> | ||
*Reduction factor for residual control that reduces head change (BACKREDUCE) – Values should be between 0.0 and 1.0, where smaller values result in smaller head-change values. Only read if residual control is active. | *''Max number of reductions (backtracks) in head change (MAXBACKITER)'' – A value between 10 and 50 works well. Only read if residual control is active. | ||
*''Proportional decrease in root-mean-squared error (BACKTOL)'' – Only read if residual control is active. | |||
*''Reduction factor for residual control that reduces head change (BACKREDUCE)'' – Values should be between 0.0 and 1.0, where smaller values result in smaller head-change values. Only read if residual control is active. | |||
==GMRES Specified Options== | ==GMRES Specified Options== | ||
*Max number of iterations for the linear solution (MAXITINNER) | *''Max number of iterations for the linear solution (MAXITINNER)'' – This value is the maximum number of iterations per call to the solver. | ||
*Method of incomplete factorization used as preconditioner (ILUMETHOD) – The index for selection of the method for incomplete factorization (ILU) used as a preconditioner. | *''Method of incomplete factorization used as preconditioner (ILUMETHOD)'' – The index for selection of the method for incomplete factorization (ILU) used as a preconditioner. | ||
<blockquote style="margin-top:0px; margin-bottom:0px;"> | |||
* (1) ILU with drop tolerance and fill limit | |||
*Fill limit for ILUMETHOD 1 or level of fill for ILUMETHOD 2 (LEVFILL) | * (2) ILU(k), Order k incomplete LU factorization | ||
*Tolerance for convergence of linear solver (STOPTOL) | </blockquote> | ||
*Number of iterations between restarts of GMRES (MSDR) | *''Fill limit for ILUMETHOD 1 or level of fill for ILUMETHOD 2 (LEVFILL)'' – Recommended values: 5–10 for method 1, 0–2 for method 2. | ||
*''Tolerance for convergence of linear solver (STOPTOL)'' – This is the residual of the linear equations scaled by the norm of the root mean squared error. | |||
*''Number of iterations between restarts of GMRES (MSDR)'' | |||
==χMD Specified Options== | ==χMD Specified Options== | ||
*Acceleration method (IACL) | *''Acceleration method (IACL)'' – A flag for the acceleration method: | ||
*Scheme of ordering unknowns (NORDER) | <blockquote style="margin-top:0px; margin-bottom:0px;"> | ||
*Level of fill for incomplete LU factorization (LEVEL) | * (0) conjugate gradient | ||
*Number of orthogonalization for the ORTHOMIN acceleration scheme (NORTH) | * (1) ORTHOMIN | ||
*Reduced system preconditioning (IREDSYS) | * (2) Bi-CGSTAB | ||
*Use drop tolerance in preconditioning (IDROPTOL) | </blockquote> | ||
*Drop tolerance for preconditioning (EPSRN) | *''Scheme of ordering unknowns (NORDER)'' – A flag with the following options: | ||
*Head closure criteria for inner (linear) iterations (HCLOSEXMD) | <blockquote style="margin-top:0px; margin-bottom:0px;"> | ||
*Max number of iterations for linear solution (MXITERXMD) | * (0) original ordering | ||
* (1) RCM ordering | |||
* (2) Minimum Degree ordering | |||
</blockquote> | |||
*''Level of fill for incomplete LU factorization (LEVEL)'' | |||
*''Number of orthogonalization for the ORTHOMIN acceleration scheme (NORTH)'' – A number between 4 and 10 is appropriate. Small values require less storage but more iterations may be required. Should equal 2 for the other acceleration methods. | |||
*''Reduced system preconditioning (IREDSYS)'' – A flag for reduced system preconditioning. | |||
<blockquote style="margin-top:0px; margin-bottom:0px;"> | |||
* (0) do not apply | |||
* (1) apply | |||
</blockquote> | |||
* ''Residual reduction-convergence criteria (RRCTOLS)'' | |||
*''Use drop tolerance in preconditioning (IDROPTOL)'' – A flag for using drop tolerance in the preconditioning. | |||
<blockquote style="margin-top:0px; margin-bottom:0px;"> | |||
* 0 = don't use | |||
* 1 = use | |||
</blockquote> | |||
*''Drop tolerance for preconditioning (EPSRN)'' | |||
*''Head closure criteria for inner (linear) iterations (HCLOSEXMD)'' | |||
*''Max number of iterations for linear solution (MXITERXMD)'' | |||
==References== | ==References== | ||
For more information on the NWT package see the USGS documentation at: [http://water.usgs.gov/nrp/gwsoftware/modflow2000/MFDOC/nwt_newton_solver.htm water.usgs.gov/nrp/gwsoftware/modflow2000/MFDOC/nwt_newton_solver.htm] | For more information on the NWT package see the USGS documentation at: [http://water.usgs.gov/nrp/gwsoftware/modflow2000/MFDOC/nwt_newton_solver.htm water.usgs.gov/nrp/gwsoftware/modflow2000/MFDOC/nwt_newton_solver.htm] | ||
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{{Navbox GMS}} | {{Navbox GMS}} | ||
[[Category:MODFLOW]] | [[Category:MODFLOW]] | ||
