Actual source code: ex1f.F90
petsc-3.13.6 2020-09-29
1: !
2: !
3: ! Description: Uses the Newton method to solve a two-variable system.
4: !
5: !!/*T
6: ! Concepts: SNES^basic uniprocessor example
7: ! Processors: 1
8: !T*/
11: !
12: ! -----------------------------------------------------------------------
14: program main
15: #include <petsc/finclude/petsc.h>
16: use petsc
17: implicit none
20: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
21: ! Variable declarations
22: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
23: !
24: ! Variables:
25: ! snes - nonlinear solver
26: ! ksp - linear solver
27: ! pc - preconditioner context
28: ! ksp - Krylov subspace method context
29: ! x, r - solution, residual vectors
30: ! J - Jacobian matrix
31: ! its - iterations for convergence
32: !
33: SNES snes
34: PC pc
35: KSP ksp
36: Vec x,r
37: Mat J
38: SNESLineSearch linesearch
39: PetscErrorCode ierr
40: PetscInt its,i2,i20
41: PetscMPIInt size,rank
42: PetscScalar pfive
43: PetscReal tol
44: PetscBool setls
45: PetscViewer viewer
46: double precision threshold,oldthreshold
48: ! Note: Any user-defined Fortran routines (such as FormJacobian)
49: ! MUST be declared as external.
51: external FormFunction, FormJacobian, MyLineSearch
53: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
54: ! Macro definitions
55: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
56: !
57: ! Macros to make clearer the process of setting values in vectors and
58: ! getting values from vectors. These vectors are used in the routines
59: ! FormFunction() and FormJacobian().
60: ! - The element lx_a(ib) is element ib in the vector x
61: !
62: #define lx_a(ib) lx_v(lx_i + (ib))
63: #define lf_a(ib) lf_v(lf_i + (ib))
64: !
65: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
66: ! Beginning of program
67: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
69: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
70: if (ierr .ne. 0) then
71: print*,'Unable to initialize PETSc'
72: stop
73: endif
74: call PetscLogNestedBegin(ierr);CHKERRA(ierr)
75: threshold = 1.0
76: call PetscLogSetThreshold(threshold,oldthreshold,ierr)
77: ! dummy test of logging a reduction
78: PetscAReduce()
79: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
80: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
81: if (size .ne. 1) then; SETERRA(PETSC_COMM_SELF,PETSC_ERR_WRONG_MPI_SIZE,'Uniprocessor example'); endif
83: i2 = 2
84: i20 = 20
85: ! - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - -
86: ! Create nonlinear solver context
87: ! - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - -
89: call SNESCreate(PETSC_COMM_WORLD,snes,ierr)
91: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
92: ! Create matrix and vector data structures; set corresponding routines
93: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
95: ! Create vectors for solution and nonlinear function
97: call VecCreateSeq(PETSC_COMM_SELF,i2,x,ierr)
98: call VecDuplicate(x,r,ierr)
100: ! Create Jacobian matrix data structure
102: call MatCreate(PETSC_COMM_SELF,J,ierr)
103: call MatSetSizes(J,PETSC_DECIDE,PETSC_DECIDE,i2,i2,ierr)
104: call MatSetFromOptions(J,ierr)
105: call MatSetUp(J,ierr)
107: ! Set function evaluation routine and vector
109: call SNESSetFunction(snes,r,FormFunction,0,ierr)
111: ! Set Jacobian matrix data structure and Jacobian evaluation routine
113: call SNESSetJacobian(snes,J,J,FormJacobian,0,ierr)
115: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
116: ! Customize nonlinear solver; set runtime options
117: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
119: ! Set linear solver defaults for this problem. By extracting the
120: ! KSP, KSP, and PC contexts from the SNES context, we can then
121: ! directly call any KSP, KSP, and PC routines to set various options.
123: call SNESGetKSP(snes,ksp,ierr)
124: call KSPGetPC(ksp,pc,ierr)
125: call PCSetType(pc,PCNONE,ierr)
126: tol = 1.e-4
127: call KSPSetTolerances(ksp,tol,PETSC_DEFAULT_REAL, &
128: & PETSC_DEFAULT_REAL,i20,ierr)
130: ! Set SNES/KSP/KSP/PC runtime options, e.g.,
131: ! -snes_view -snes_monitor -ksp_type <ksp> -pc_type <pc>
132: ! These options will override those specified above as long as
133: ! SNESSetFromOptions() is called _after_ any other customization
134: ! routines.
137: call SNESSetFromOptions(snes,ierr)
139: call PetscOptionsHasName(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER, &
140: & '-setls',setls,ierr)
142: if (setls) then
143: call SNESGetLineSearch(snes, linesearch, ierr)
144: call SNESLineSearchSetType(linesearch, 'shell', ierr)
145: call SNESLineSearchShellSetUserFunc(linesearch, MyLineSearch, &
146: & 0, ierr)
147: endif
149: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
150: ! Evaluate initial guess; then solve nonlinear system
151: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
153: ! Note: The user should initialize the vector, x, with the initial guess
154: ! for the nonlinear solver prior to calling SNESSolve(). In particular,
155: ! to employ an initial guess of zero, the user should explicitly set
156: ! this vector to zero by calling VecSet().
158: pfive = 0.5
159: call VecSet(x,pfive,ierr)
160: call SNESSolve(snes,PETSC_NULL_VEC,x,ierr)
161: call SNESGetIterationNumber(snes,its,ierr);
162: if (rank .eq. 0) then
163: write(6,100) its
164: endif
165: 100 format('Number of SNES iterations = ',i5)
167: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
168: ! Free work space. All PETSc objects should be destroyed when they
169: ! are no longer needed.
170: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
172: call VecDestroy(x,ierr)
173: call VecDestroy(r,ierr)
174: call MatDestroy(J,ierr)
175: call SNESDestroy(snes,ierr)
176: call PetscViewerASCIIOpen(PETSC_COMM_WORLD,'filename.xml',viewer,ierr)
177: call PetscViewerPushFormat(viewer,PETSC_VIEWER_ASCII_XML,ierr)
178: call PetscLogView(viewer,ierr)
179: call PetscViewerDestroy(viewer,ierr)
180: call PetscFinalize(ierr)
181: end
182: !
183: ! ------------------------------------------------------------------------
184: !
185: ! FormFunction - Evaluates nonlinear function, F(x).
186: !
187: ! Input Parameters:
188: ! snes - the SNES context
189: ! x - input vector
190: ! dummy - optional user-defined context (not used here)
191: !
192: ! Output Parameter:
193: ! f - function vector
194: !
195: subroutine FormFunction(snes,x,f,dummy,ierr)
196: use petscsnes
197: implicit none
199: SNES snes
200: Vec x,f
201: PetscErrorCode ierr
202: integer dummy(*)
204: ! Declarations for use with local arrays
206: PetscScalar lx_v(2),lf_v(2)
207: PetscOffset lx_i,lf_i
209: ! Get pointers to vector data.
210: ! - For default PETSc vectors, VecGetArray() returns a pointer to
211: ! the data array. Otherwise, the routine is implementation dependent.
212: ! - You MUST call VecRestoreArray() when you no longer need access to
213: ! the array.
214: ! - Note that the Fortran interface to VecGetArray() differs from the
215: ! C version. See the Fortran chapter of the users manual for details.
217: call VecGetArrayRead(x,lx_v,lx_i,ierr)
218: call VecGetArray(f,lf_v,lf_i,ierr)
220: ! Compute function
222: lf_a(1) = lx_a(1)*lx_a(1) &
223: & + lx_a(1)*lx_a(2) - 3.0
224: lf_a(2) = lx_a(1)*lx_a(2) &
225: & + lx_a(2)*lx_a(2) - 6.0
227: ! Restore vectors
229: call VecRestoreArrayRead(x,lx_v,lx_i,ierr)
230: call VecRestoreArray(f,lf_v,lf_i,ierr)
232: return
233: end
235: ! ---------------------------------------------------------------------
236: !
237: ! FormJacobian - Evaluates Jacobian matrix.
238: !
239: ! Input Parameters:
240: ! snes - the SNES context
241: ! x - input vector
242: ! dummy - optional user-defined context (not used here)
243: !
244: ! Output Parameters:
245: ! A - Jacobian matrix
246: ! B - optionally different preconditioning matrix
247: ! flag - flag indicating matrix structure
248: !
249: subroutine FormJacobian(snes,X,jac,B,dummy,ierr)
250: use petscsnes
251: implicit none
253: SNES snes
254: Vec X
255: Mat jac,B
256: PetscScalar A(4)
257: PetscErrorCode ierr
258: PetscInt idx(2),i2
259: integer dummy(*)
261: ! Declarations for use with local arrays
263: PetscScalar lx_v(2)
264: PetscOffset lx_i
266: ! Get pointer to vector data
268: i2 = 2
269: call VecGetArrayRead(x,lx_v,lx_i,ierr)
271: ! Compute Jacobian entries and insert into matrix.
272: ! - Since this is such a small problem, we set all entries for
273: ! the matrix at once.
274: ! - Note that MatSetValues() uses 0-based row and column numbers
275: ! in Fortran as well as in C (as set here in the array idx).
277: idx(1) = 0
278: idx(2) = 1
279: A(1) = 2.0*lx_a(1) + lx_a(2)
280: A(2) = lx_a(1)
281: A(3) = lx_a(2)
282: A(4) = lx_a(1) + 2.0*lx_a(2)
283: call MatSetValues(B,i2,idx,i2,idx,A,INSERT_VALUES,ierr)
285: ! Restore vector
287: call VecRestoreArrayRead(x,lx_v,lx_i,ierr)
289: ! Assemble matrix
291: call MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY,ierr)
292: call MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY,ierr)
293: if (B .ne. jac) then
294: call MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY,ierr)
295: call MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY,ierr)
296: endif
298: return
299: end
302: subroutine MyLineSearch(linesearch, lctx, ierr)
303: use petscsnes
304: implicit none
306: SNESLineSearch linesearch
307: SNES snes
308: integer lctx
309: Vec x, f,g, y, w
310: PetscReal ynorm,gnorm,xnorm
311: PetscBool flag
312: PetscErrorCode ierr
314: PetscScalar mone
316: mone = -1.0
317: call SNESLineSearchGetSNES(linesearch, snes, ierr)
318: call SNESLineSearchGetVecs(linesearch, x, f, y, w, g, ierr)
319: call VecNorm(y,NORM_2,ynorm,ierr)
320: call VecAXPY(x,mone,y,ierr)
321: call SNESComputeFunction(snes,x,f,ierr)
322: call VecNorm(f,NORM_2,gnorm,ierr)
323: call VecNorm(x,NORM_2,xnorm,ierr)
324: call VecNorm(y,NORM_2,ynorm,ierr)
325: call SNESLineSearchSetNorms(linesearch, xnorm, gnorm, ynorm, &
326: & ierr)
327: flag = PETSC_FALSE
328: return
329: end
331: !/*TEST
332: !
333: ! test:
334: ! args: -ksp_gmres_cgs_refinement_type refine_always -snes_monitor_short
335: ! requires: !single
336: !
337: !TEST*/