xref: /petsc/include/petscdt.h (revision f1580f4e3ce5d5b2393648fd039d0d41b440385d)
1 /*
2   Common tools for constructing discretizations
3 */
4 #if !defined(PETSCDT_H)
5 #define PETSCDT_H
6 
7 #include <petscsys.h>
8 
9 /* SUBMANSEC = DT */
10 
11 PETSC_EXTERN PetscClassId PETSCQUADRATURE_CLASSID;
12 
13 /*S
14   PetscQuadrature - Quadrature rule for integration.
15 
16   Level: beginner
17 
18 .seealso: `PetscQuadratureCreate()`, `PetscQuadratureDestroy()`
19 S*/
20 typedef struct _p_PetscQuadrature *PetscQuadrature;
21 
22 /*E
23   PetscGaussLobattoLegendreCreateType - algorithm used to compute the Gauss-Lobatto-Legendre nodes and weights
24 
25   Level: intermediate
26 
27 $  `PETSCGAUSSLOBATTOLEGENDRE_VIA_LINEAR_ALGEBRA` - compute the nodes via linear algebra
28 $  `PETSCGAUSSLOBATTOLEGENDRE_VIA_NEWTON` - compute the nodes by solving a nonlinear equation with Newton's method
29 
30 E*/
31 typedef enum {
32   PETSCGAUSSLOBATTOLEGENDRE_VIA_LINEAR_ALGEBRA,
33   PETSCGAUSSLOBATTOLEGENDRE_VIA_NEWTON
34 } PetscGaussLobattoLegendreCreateType;
35 
36 /*E
37   PetscDTNodeType - A description of strategies for generating nodes (both
38   quadrature nodes and nodes for Lagrange polynomials)
39 
40   Level: intermediate
41 
42 $  `PETSCDTNODES_DEFAULT` - Nodes chosen by PETSc
43 $  `PETSCDTNODES_GAUSSJACOBI` - Nodes at either Gauss-Jacobi or Gauss-Lobatto-Jacobi quadrature points
44 $  `PETSCDTNODES_EQUISPACED` - Nodes equispaced either including the endpoints or excluding them
45 $  `PETSCDTNODES_TANHSINH` - Nodes at Tanh-Sinh quadrature points
46 
47   Note:
48   A `PetscDTNodeType` can be paired with a `PetscBool` to indicate whether
49   the nodes include endpoints or not, and in the case of `PETSCDT_GAUSSJACOBI`
50   with exponents for the weight function.
51 
52 E*/
53 typedef enum {
54   PETSCDTNODES_DEFAULT = -1,
55   PETSCDTNODES_GAUSSJACOBI,
56   PETSCDTNODES_EQUISPACED,
57   PETSCDTNODES_TANHSINH
58 } PetscDTNodeType;
59 
60 PETSC_EXTERN const char *const *const PetscDTNodeTypes;
61 
62 /*E
63   PetscDTSimplexQuadratureType - A description of classes of quadrature rules for simplices
64 
65   Level: intermediate
66 
67 $  `PETSCDTSIMPLEXQUAD_DEFAULT` - Quadrature rule chosen by PETSc
68 $  `PETSCDTSIMPLEXQUAD_CONIC`   - Quadrature rules constructed as
69                                 conically-warped tensor products of 1D
70                                 Gauss-Jacobi quadrature rules.  These are
71                                 explicitly computable in any dimension for any
72                                 degree, and the tensor-product structure can be
73                                 exploited by sum-factorization methods, but
74                                 they are not efficient in terms of nodes per
75                                 polynomial degree.
76 $  `PETSCDTSIMPLEXQUAD_MINSYM`  - Quadrature rules that are fully symmetric
77                                 (symmetries of the simplex preserve the nodes
78                                 and weights) with minimal (or near minimal)
79                                 number of nodes.  In dimensions higher than 1
80                                 these are not simple to compute, so lookup
81                                 tables are used.
82 
83 .seealso: `PetscDTSimplexQuadrature()`
84 E*/
85 typedef enum {
86   PETSCDTSIMPLEXQUAD_DEFAULT = -1,
87   PETSCDTSIMPLEXQUAD_CONIC   = 0,
88   PETSCDTSIMPLEXQUAD_MINSYM
89 } PetscDTSimplexQuadratureType;
90 
91 PETSC_EXTERN const char *const *const PetscDTSimplexQuadratureTypes;
92 
93 PETSC_EXTERN PetscErrorCode PetscQuadratureCreate(MPI_Comm, PetscQuadrature *);
94 PETSC_EXTERN PetscErrorCode PetscQuadratureDuplicate(PetscQuadrature, PetscQuadrature *);
95 PETSC_EXTERN PetscErrorCode PetscQuadratureGetOrder(PetscQuadrature, PetscInt *);
96 PETSC_EXTERN PetscErrorCode PetscQuadratureSetOrder(PetscQuadrature, PetscInt);
97 PETSC_EXTERN PetscErrorCode PetscQuadratureGetNumComponents(PetscQuadrature, PetscInt *);
98 PETSC_EXTERN PetscErrorCode PetscQuadratureSetNumComponents(PetscQuadrature, PetscInt);
99 PETSC_EXTERN PetscErrorCode PetscQuadratureEqual(PetscQuadrature, PetscQuadrature, PetscBool *);
100 PETSC_EXTERN PetscErrorCode PetscQuadratureGetData(PetscQuadrature, PetscInt *, PetscInt *, PetscInt *, const PetscReal *[], const PetscReal *[]);
101 PETSC_EXTERN PetscErrorCode PetscQuadratureSetData(PetscQuadrature, PetscInt, PetscInt, PetscInt, const PetscReal[], const PetscReal[]);
102 PETSC_EXTERN PetscErrorCode PetscQuadratureView(PetscQuadrature, PetscViewer);
103 PETSC_EXTERN PetscErrorCode PetscQuadratureDestroy(PetscQuadrature *);
104 
105 PETSC_EXTERN PetscErrorCode PetscDTTensorQuadratureCreate(PetscQuadrature, PetscQuadrature, PetscQuadrature *);
106 PETSC_EXTERN PetscErrorCode PetscQuadratureExpandComposite(PetscQuadrature, PetscInt, const PetscReal[], const PetscReal[], PetscQuadrature *);
107 
108 PETSC_EXTERN PetscErrorCode PetscQuadraturePushForward(PetscQuadrature, PetscInt, const PetscReal[], const PetscReal[], const PetscReal[], PetscInt, PetscQuadrature *);
109 
110 PETSC_EXTERN PetscErrorCode PetscDTLegendreEval(PetscInt, const PetscReal *, PetscInt, const PetscInt *, PetscReal *, PetscReal *, PetscReal *);
111 PETSC_EXTERN PetscErrorCode PetscDTJacobiNorm(PetscReal, PetscReal, PetscInt, PetscReal *);
112 PETSC_EXTERN PetscErrorCode PetscDTJacobiEval(PetscInt, PetscReal, PetscReal, const PetscReal *, PetscInt, const PetscInt *, PetscReal *, PetscReal *, PetscReal *);
113 PETSC_EXTERN PetscErrorCode PetscDTJacobiEvalJet(PetscReal, PetscReal, PetscInt, const PetscReal[], PetscInt, PetscInt, PetscReal[]);
114 PETSC_EXTERN PetscErrorCode PetscDTPKDEvalJet(PetscInt, PetscInt, const PetscReal[], PetscInt, PetscInt, PetscReal[]);
115 PETSC_EXTERN PetscErrorCode PetscDTPTrimmedSize(PetscInt, PetscInt, PetscInt, PetscInt *);
116 PETSC_EXTERN PetscErrorCode PetscDTPTrimmedEvalJet(PetscInt, PetscInt, const PetscReal[], PetscInt, PetscInt, PetscInt, PetscReal[]);
117 PETSC_EXTERN PetscErrorCode PetscDTGaussQuadrature(PetscInt, PetscReal, PetscReal, PetscReal *, PetscReal *);
118 PETSC_EXTERN PetscErrorCode PetscDTGaussJacobiQuadrature(PetscInt, PetscReal, PetscReal, PetscReal, PetscReal, PetscReal *, PetscReal *);
119 PETSC_EXTERN PetscErrorCode PetscDTGaussLobattoJacobiQuadrature(PetscInt, PetscReal, PetscReal, PetscReal, PetscReal, PetscReal *, PetscReal *);
120 PETSC_EXTERN PetscErrorCode PetscDTGaussLobattoLegendreQuadrature(PetscInt, PetscGaussLobattoLegendreCreateType, PetscReal *, PetscReal *);
121 PETSC_EXTERN PetscErrorCode PetscDTReconstructPoly(PetscInt, PetscInt, const PetscReal *, PetscInt, const PetscReal *, PetscReal *);
122 PETSC_EXTERN PetscErrorCode PetscDTGaussTensorQuadrature(PetscInt, PetscInt, PetscInt, PetscReal, PetscReal, PetscQuadrature *);
123 PETSC_EXTERN PetscErrorCode PetscDTStroudConicalQuadrature(PetscInt, PetscInt, PetscInt, PetscReal, PetscReal, PetscQuadrature *);
124 PETSC_EXTERN PetscErrorCode PetscDTSimplexQuadrature(PetscInt, PetscInt, PetscDTSimplexQuadratureType, PetscQuadrature *);
125 
126 PETSC_EXTERN PetscErrorCode PetscDTTanhSinhTensorQuadrature(PetscInt, PetscInt, PetscReal, PetscReal, PetscQuadrature *);
127 PETSC_EXTERN PetscErrorCode PetscDTTanhSinhIntegrate(void (*)(const PetscReal[], void *, PetscReal *), PetscReal, PetscReal, PetscInt, void *, PetscReal *);
128 PETSC_EXTERN PetscErrorCode PetscDTTanhSinhIntegrateMPFR(void (*)(const PetscReal[], void *, PetscReal *), PetscReal, PetscReal, PetscInt, void *, PetscReal *);
129 
130 PETSC_EXTERN PetscErrorCode PetscGaussLobattoLegendreIntegrate(PetscInt, PetscReal *, PetscReal *, const PetscReal *, PetscReal *);
131 PETSC_EXTERN PetscErrorCode PetscGaussLobattoLegendreElementLaplacianCreate(PetscInt, PetscReal *, PetscReal *, PetscReal ***);
132 PETSC_EXTERN PetscErrorCode PetscGaussLobattoLegendreElementLaplacianDestroy(PetscInt, PetscReal *, PetscReal *, PetscReal ***);
133 PETSC_EXTERN PetscErrorCode PetscGaussLobattoLegendreElementGradientCreate(PetscInt, PetscReal *, PetscReal *, PetscReal ***, PetscReal ***);
134 PETSC_EXTERN PetscErrorCode PetscGaussLobattoLegendreElementGradientDestroy(PetscInt, PetscReal *, PetscReal *, PetscReal ***, PetscReal ***);
135 PETSC_EXTERN PetscErrorCode PetscGaussLobattoLegendreElementAdvectionCreate(PetscInt, PetscReal *, PetscReal *, PetscReal ***);
136 PETSC_EXTERN PetscErrorCode PetscGaussLobattoLegendreElementAdvectionDestroy(PetscInt, PetscReal *, PetscReal *, PetscReal ***);
137 PETSC_EXTERN PetscErrorCode PetscGaussLobattoLegendreElementMassCreate(PetscInt, PetscReal *, PetscReal *, PetscReal ***);
138 PETSC_EXTERN PetscErrorCode PetscGaussLobattoLegendreElementMassDestroy(PetscInt, PetscReal *, PetscReal *, PetscReal ***);
139 
140 PETSC_EXTERN PetscErrorCode PetscDTAltVApply(PetscInt, PetscInt, const PetscReal *, const PetscReal *, PetscReal *);
141 PETSC_EXTERN PetscErrorCode PetscDTAltVWedge(PetscInt, PetscInt, PetscInt, const PetscReal *, const PetscReal *, PetscReal *);
142 PETSC_EXTERN PetscErrorCode PetscDTAltVWedgeMatrix(PetscInt, PetscInt, PetscInt, const PetscReal *, PetscReal *);
143 PETSC_EXTERN PetscErrorCode PetscDTAltVPullback(PetscInt, PetscInt, const PetscReal *, PetscInt, const PetscReal *, PetscReal *);
144 PETSC_EXTERN PetscErrorCode PetscDTAltVPullbackMatrix(PetscInt, PetscInt, const PetscReal *, PetscInt, PetscReal *);
145 PETSC_EXTERN PetscErrorCode PetscDTAltVInterior(PetscInt, PetscInt, const PetscReal *, const PetscReal *, PetscReal *);
146 PETSC_EXTERN PetscErrorCode PetscDTAltVInteriorMatrix(PetscInt, PetscInt, const PetscReal *, PetscReal *);
147 PETSC_EXTERN PetscErrorCode PetscDTAltVInteriorPattern(PetscInt, PetscInt, PetscInt (*)[3]);
148 PETSC_EXTERN PetscErrorCode PetscDTAltVStar(PetscInt, PetscInt, PetscInt, const PetscReal *, PetscReal *);
149 
150 PETSC_EXTERN PetscErrorCode PetscDTBaryToIndex(PetscInt, PetscInt, const PetscInt[], PetscInt *);
151 PETSC_EXTERN PetscErrorCode PetscDTIndexToBary(PetscInt, PetscInt, PetscInt, PetscInt[]);
152 PETSC_EXTERN PetscErrorCode PetscDTGradedOrderToIndex(PetscInt, const PetscInt[], PetscInt *);
153 PETSC_EXTERN PetscErrorCode PetscDTIndexToGradedOrder(PetscInt, PetscInt, PetscInt[]);
154 
155 #if defined(PETSC_USE_64BIT_INDICES)
156 #define PETSC_FACTORIAL_MAX 20
157 #define PETSC_BINOMIAL_MAX  61
158 #else
159 #define PETSC_FACTORIAL_MAX 12
160 #define PETSC_BINOMIAL_MAX  29
161 #endif
162 
163 /*MC
164    PetscDTFactorial - Approximate n! as a real number
165 
166    Input Parameter:
167 .  n - a non-negative integer
168 
169    Output Parameter:
170 .  factorial - n!
171 
172    Level: beginner
173 M*/
174 static inline PetscErrorCode PetscDTFactorial(PetscInt n, PetscReal *factorial) {
175   PetscReal f = 1.0;
176 
177   PetscFunctionBegin;
178   *factorial = -1.0;
179   PetscCheck(n >= 0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Factorial called with negative number %" PetscInt_FMT, n);
180   for (PetscInt i = 1; i < n + 1; ++i) f *= (PetscReal)i;
181   *factorial = f;
182   PetscFunctionReturn(0);
183 }
184 
185 /*MC
186    PetscDTFactorialInt - Compute n! as an integer
187 
188    Input Parameter:
189 .  n - a non-negative integer
190 
191    Output Parameter:
192 .  factorial - n!
193 
194    Level: beginner
195 
196    Note: this is limited to n such that n! can be represented by PetscInt, which is 12 if PetscInt is a signed 32-bit integer and 20 if PetscInt is a signed 64-bit integer.
197 M*/
198 static inline PetscErrorCode PetscDTFactorialInt(PetscInt n, PetscInt *factorial) {
199   PetscInt facLookup[13] = {1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600};
200 
201   PetscFunctionBegin;
202   *factorial = -1;
203   PetscCheck(n >= 0 && n <= PETSC_FACTORIAL_MAX, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Number of elements %" PetscInt_FMT " is not in supported range [0,%d]", n, PETSC_FACTORIAL_MAX);
204   if (n <= 12) {
205     *factorial = facLookup[n];
206   } else {
207     PetscInt f = facLookup[12];
208     PetscInt i;
209 
210     for (i = 13; i < n + 1; ++i) f *= i;
211     *factorial = f;
212   }
213   PetscFunctionReturn(0);
214 }
215 
216 /*MC
217    PetscDTBinomial - Approximate the binomial coefficient "n choose k"
218 
219    Input Parameters:
220 +  n - a non-negative integer
221 -  k - an integer between 0 and n, inclusive
222 
223    Output Parameter:
224 .  binomial - approximation of the binomial coefficient n choose k
225 
226    Level: beginner
227 M*/
228 static inline PetscErrorCode PetscDTBinomial(PetscInt n, PetscInt k, PetscReal *binomial) {
229   PetscFunctionBeginHot;
230   *binomial = -1.0;
231   PetscCheck(n >= 0 && k >= 0 && k <= n, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Binomial arguments (%" PetscInt_FMT " %" PetscInt_FMT ") must be non-negative, k <= n", n, k);
232   if (n <= 3) {
233     PetscInt binomLookup[4][4] = {
234       {1, 0, 0, 0},
235       {1, 1, 0, 0},
236       {1, 2, 1, 0},
237       {1, 3, 3, 1}
238     };
239 
240     *binomial = (PetscReal)binomLookup[n][k];
241   } else {
242     PetscReal binom = 1.0;
243 
244     k = PetscMin(k, n - k);
245     for (PetscInt i = 0; i < k; i++) binom = (binom * (PetscReal)(n - i)) / (PetscReal)(i + 1);
246     *binomial = binom;
247   }
248   PetscFunctionReturn(0);
249 }
250 
251 /*MC
252    PetscDTBinomialInt - Compute the binomial coefficient "n choose k"
253 
254    Input Parameters:
255 +  n - a non-negative integer
256 -  k - an integer between 0 and n, inclusive
257 
258    Output Parameter:
259 .  binomial - the binomial coefficient n choose k
260 
261    Note: this is limited by integers that can be represented by `PetscInt`
262 
263    Level: beginner
264 M*/
265 static inline PetscErrorCode PetscDTBinomialInt(PetscInt n, PetscInt k, PetscInt *binomial) {
266   PetscInt bin;
267 
268   PetscFunctionBegin;
269   *binomial = -1;
270   PetscCheck(n >= 0 && k >= 0 && k <= n, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Binomial arguments (%" PetscInt_FMT " %" PetscInt_FMT ") must be non-negative, k <= n", n, k);
271   PetscCheck(n <= PETSC_BINOMIAL_MAX, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Binomial elements %" PetscInt_FMT " is larger than max for PetscInt, %d", n, PETSC_BINOMIAL_MAX);
272   if (n <= 3) {
273     PetscInt binomLookup[4][4] = {
274       {1, 0, 0, 0},
275       {1, 1, 0, 0},
276       {1, 2, 1, 0},
277       {1, 3, 3, 1}
278     };
279 
280     bin = binomLookup[n][k];
281   } else {
282     PetscInt binom = 1;
283 
284     k = PetscMin(k, n - k);
285     for (PetscInt i = 0; i < k; i++) binom = (binom * (n - i)) / (i + 1);
286     bin = binom;
287   }
288   *binomial = bin;
289   PetscFunctionReturn(0);
290 }
291 
292 /*MC
293    PetscDTEnumPerm - Get a permutation of n integers from its encoding into the integers [0, n!) as a sequence of swaps.
294 
295    A permutation can be described by the operations that convert the lists [0, 1, ..., n-1] into the permutation,
296    by a sequence of swaps, where the ith step swaps whatever number is in ith position with a number that is in
297    some position j >= i.  This swap is encoded as the difference (j - i).  The difference d_i at step i is less than
298    (n - i).  This sequence of n-1 differences [d_0, ..., d_{n-2}] is encoded as the number
299    (n-1)! * d_0 + (n-2)! * d_1 + ... + 1! * d_{n-2}.
300 
301    Input Parameters:
302 +  n - a non-negative integer (see note about limits below)
303 -  k - an integer in [0, n!)
304 
305    Output Parameters:
306 +  perm - the permuted list of the integers [0, ..., n-1]
307 -  isOdd - if not NULL, returns wether the permutation used an even or odd number of swaps.
308 
309    Note:
310    Limited to n such that n! can be represented by `PetscInt`, which is 12 if `PetscInt` is a signed 32-bit integer and 20 if `PetscInt` is a signed 64-bit integer.
311 
312    Level: beginner
313 M*/
314 static inline PetscErrorCode PetscDTEnumPerm(PetscInt n, PetscInt k, PetscInt *perm, PetscBool *isOdd) {
315   PetscInt  odd = 0;
316   PetscInt  i;
317   PetscInt  work[PETSC_FACTORIAL_MAX];
318   PetscInt *w;
319 
320   PetscFunctionBegin;
321   if (isOdd) *isOdd = PETSC_FALSE;
322   PetscCheck(n >= 0 && n <= PETSC_FACTORIAL_MAX, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Number of elements %" PetscInt_FMT " is not in supported range [0,%d]", n, PETSC_FACTORIAL_MAX);
323   w = &work[n - 2];
324   for (i = 2; i <= n; i++) {
325     *(w--) = k % i;
326     k /= i;
327   }
328   for (i = 0; i < n; i++) perm[i] = i;
329   for (i = 0; i < n - 1; i++) {
330     PetscInt s    = work[i];
331     PetscInt swap = perm[i];
332 
333     perm[i]     = perm[i + s];
334     perm[i + s] = swap;
335     odd ^= (!!s);
336   }
337   if (isOdd) *isOdd = odd ? PETSC_TRUE : PETSC_FALSE;
338   PetscFunctionReturn(0);
339 }
340 
341 /*MC
342    PetscDTPermIndex - Encode a permutation of n into an integer in [0, n!).  This inverts `PetscDTEnumPerm`.
343 
344    Input Parameters:
345 +  n - a non-negative integer (see note about limits below)
346 -  perm - the permuted list of the integers [0, ..., n-1]
347 
348    Output Parameters:
349 +  k - an integer in [0, n!)
350 -  isOdd - if not NULL, returns wether the permutation used an even or odd number of swaps.
351 
352    Note:
353    Limited to n such that n! can be represented by `PetscInt`, which is 12 if `PetscInt` is a signed 32-bit integer and 20 if `PetscInt` is a signed 64-bit integer.
354 
355    Level: beginner
356 M*/
357 static inline PetscErrorCode PetscDTPermIndex(PetscInt n, const PetscInt *perm, PetscInt *k, PetscBool *isOdd) {
358   PetscInt odd = 0;
359   PetscInt i, idx;
360   PetscInt work[PETSC_FACTORIAL_MAX];
361   PetscInt iwork[PETSC_FACTORIAL_MAX];
362 
363   PetscFunctionBeginHot;
364   *k = -1;
365   if (isOdd) *isOdd = PETSC_FALSE;
366   PetscCheck(n >= 0 && n <= PETSC_FACTORIAL_MAX, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Number of elements %" PetscInt_FMT " is not in supported range [0,%d]", n, PETSC_FACTORIAL_MAX);
367   for (i = 0; i < n; i++) work[i] = i;  /* partial permutation */
368   for (i = 0; i < n; i++) iwork[i] = i; /* partial permutation inverse */
369   for (idx = 0, i = 0; i < n - 1; i++) {
370     PetscInt j    = perm[i];
371     PetscInt icur = work[i];
372     PetscInt jloc = iwork[j];
373     PetscInt diff = jloc - i;
374 
375     idx         = idx * (n - i) + diff;
376     /* swap (i, jloc) */
377     work[i]     = j;
378     work[jloc]  = icur;
379     iwork[j]    = i;
380     iwork[icur] = jloc;
381     odd ^= (!!diff);
382   }
383   *k = idx;
384   if (isOdd) *isOdd = odd ? PETSC_TRUE : PETSC_FALSE;
385   PetscFunctionReturn(0);
386 }
387 
388 /*MC
389    PetscDTEnumSubset - Get an ordered subset of the integers [0, ..., n - 1] from its encoding as an integers in [0, n choose k).
390    The encoding is in lexicographic order.
391 
392    Input Parameters:
393 +  n - a non-negative integer (see note about limits below)
394 .  k - an integer in [0, n]
395 -  j - an index in [0, n choose k)
396 
397    Output Parameter:
398 .  subset - the jth subset of size k of the integers [0, ..., n - 1]
399 
400    Note:
401    Limited by arguments such that n choose k can be represented by `PetscInt`
402 
403    Level: beginner
404 
405 .seealso: `PetscDTSubsetIndex()`
406 M*/
407 static inline PetscErrorCode PetscDTEnumSubset(PetscInt n, PetscInt k, PetscInt j, PetscInt *subset) {
408   PetscInt Nk;
409 
410   PetscFunctionBeginHot;
411   PetscCall(PetscDTBinomialInt(n, k, &Nk));
412   for (PetscInt i = 0, l = 0; i < n && l < k; i++) {
413     PetscInt Nminuskminus = (Nk * (k - l)) / (n - i);
414     PetscInt Nminusk      = Nk - Nminuskminus;
415 
416     if (j < Nminuskminus) {
417       subset[l++] = i;
418       Nk          = Nminuskminus;
419     } else {
420       j -= Nminuskminus;
421       Nk = Nminusk;
422     }
423   }
424   PetscFunctionReturn(0);
425 }
426 
427 /*MC
428    PetscDTSubsetIndex - Convert an ordered subset of k integers from the set [0, ..., n - 1] to its encoding as an integers in [0, n choose k) in lexicographic order.
429    This is the inverse of `PetscDTEnumSubset`.
430 
431    Input Parameters:
432 +  n - a non-negative integer (see note about limits below)
433 .  k - an integer in [0, n]
434 -  subset - an ordered subset of the integers [0, ..., n - 1]
435 
436    Output Parameter:
437 .  index - the rank of the subset in lexicographic order
438 
439    Note:
440    Limited by arguments such that n choose k can be represented by `PetscInt`
441 
442    Level: beginner
443 
444 .seealso: `PetscDTEnumSubset()`
445 M*/
446 static inline PetscErrorCode PetscDTSubsetIndex(PetscInt n, PetscInt k, const PetscInt *subset, PetscInt *index) {
447   PetscInt j = 0, Nk;
448 
449   PetscFunctionBegin;
450   *index = -1;
451   PetscCall(PetscDTBinomialInt(n, k, &Nk));
452   for (PetscInt i = 0, l = 0; i < n && l < k; i++) {
453     PetscInt Nminuskminus = (Nk * (k - l)) / (n - i);
454     PetscInt Nminusk      = Nk - Nminuskminus;
455 
456     if (subset[l] == i) {
457       l++;
458       Nk = Nminuskminus;
459     } else {
460       j += Nminuskminus;
461       Nk = Nminusk;
462     }
463   }
464   *index = j;
465   PetscFunctionReturn(0);
466 }
467 
468 /*MC
469    PetscDTEnumSubset - Split the integers [0, ..., n - 1] into two complementary ordered subsets, the first subset of size k and being the jth subset of that size in lexicographic order.
470 
471    Input Parameters:
472 +  n - a non-negative integer (see note about limits below)
473 .  k - an integer in [0, n]
474 -  j - an index in [0, n choose k)
475 
476    Output Parameters:
477 +  perm - the jth subset of size k of the integers [0, ..., n - 1], followed by its complementary set.
478 -  isOdd - if not NULL, return whether perm is an even or odd permutation.
479 
480    Note:
481    Limited by arguments such that n choose k can be represented by `PetscInt`
482 
483    Level: beginner
484 
485 .seealso: `PetscDTEnumSubset()`, `PetscDTSubsetIndex()`
486 M*/
487 static inline PetscErrorCode PetscDTEnumSplit(PetscInt n, PetscInt k, PetscInt j, PetscInt *perm, PetscBool *isOdd) {
488   PetscInt  i, l, m, Nk, odd = 0;
489   PetscInt *subcomp = perm + k;
490 
491   PetscFunctionBegin;
492   if (isOdd) *isOdd = PETSC_FALSE;
493   PetscCall(PetscDTBinomialInt(n, k, &Nk));
494   for (i = 0, l = 0, m = 0; i < n && l < k; i++) {
495     PetscInt Nminuskminus = (Nk * (k - l)) / (n - i);
496     PetscInt Nminusk      = Nk - Nminuskminus;
497 
498     if (j < Nminuskminus) {
499       perm[l++] = i;
500       Nk        = Nminuskminus;
501     } else {
502       subcomp[m++] = i;
503       j -= Nminuskminus;
504       odd ^= ((k - l) & 1);
505       Nk = Nminusk;
506     }
507   }
508   for (; i < n; i++) subcomp[m++] = i;
509   if (isOdd) *isOdd = odd ? PETSC_TRUE : PETSC_FALSE;
510   PetscFunctionReturn(0);
511 }
512 
513 struct _p_PetscTabulation {
514   PetscInt    K;    /* Indicates a k-jet, namely tabulated derivatives up to order k */
515   PetscInt    Nr;   /* The number of tabulation replicas (often 1) */
516   PetscInt    Np;   /* The number of tabulation points in a replica */
517   PetscInt    Nb;   /* The number of functions tabulated */
518   PetscInt    Nc;   /* The number of function components */
519   PetscInt    cdim; /* The coordinate dimension */
520   PetscReal **T;    /* The tabulation T[K] of functions and their derivatives
521                        T[0] = B[Nr*Np][Nb][Nc]:             The basis function values at quadrature points
522                        T[1] = D[Nr*Np][Nb][Nc][cdim]:       The basis function derivatives at quadrature points
523                        T[2] = H[Nr*Np][Nb][Nc][cdim][cdim]: The basis function second derivatives at quadrature points */
524 };
525 typedef struct _p_PetscTabulation *PetscTabulation;
526 
527 typedef PetscErrorCode (*PetscProbFunc)(const PetscReal[], const PetscReal[], PetscReal[]);
528 
529 typedef enum {
530   DTPROB_DENSITY_CONSTANT,
531   DTPROB_DENSITY_GAUSSIAN,
532   DTPROB_DENSITY_MAXWELL_BOLTZMANN,
533   DTPROB_NUM_DENSITY
534 } DTProbDensityType;
535 PETSC_EXTERN const char *const DTProbDensityTypes[];
536 
537 PETSC_EXTERN PetscErrorCode PetscPDFMaxwellBoltzmann1D(const PetscReal[], const PetscReal[], PetscReal[]);
538 PETSC_EXTERN PetscErrorCode PetscCDFMaxwellBoltzmann1D(const PetscReal[], const PetscReal[], PetscReal[]);
539 PETSC_EXTERN PetscErrorCode PetscPDFMaxwellBoltzmann2D(const PetscReal[], const PetscReal[], PetscReal[]);
540 PETSC_EXTERN PetscErrorCode PetscCDFMaxwellBoltzmann2D(const PetscReal[], const PetscReal[], PetscReal[]);
541 PETSC_EXTERN PetscErrorCode PetscPDFMaxwellBoltzmann3D(const PetscReal[], const PetscReal[], PetscReal[]);
542 PETSC_EXTERN PetscErrorCode PetscCDFMaxwellBoltzmann3D(const PetscReal[], const PetscReal[], PetscReal[]);
543 PETSC_EXTERN PetscErrorCode PetscPDFGaussian1D(const PetscReal[], const PetscReal[], PetscReal[]);
544 PETSC_EXTERN PetscErrorCode PetscCDFGaussian1D(const PetscReal[], const PetscReal[], PetscReal[]);
545 PETSC_EXTERN PetscErrorCode PetscPDFSampleGaussian1D(const PetscReal[], const PetscReal[], PetscReal[]);
546 PETSC_EXTERN PetscErrorCode PetscPDFGaussian2D(const PetscReal[], const PetscReal[], PetscReal[]);
547 PETSC_EXTERN PetscErrorCode PetscPDFSampleGaussian2D(const PetscReal[], const PetscReal[], PetscReal[]);
548 PETSC_EXTERN PetscErrorCode PetscPDFGaussian3D(const PetscReal[], const PetscReal[], PetscReal[]);
549 PETSC_EXTERN PetscErrorCode PetscPDFSampleGaussian3D(const PetscReal[], const PetscReal[], PetscReal[]);
550 PETSC_EXTERN PetscErrorCode PetscPDFConstant1D(const PetscReal[], const PetscReal[], PetscReal[]);
551 PETSC_EXTERN PetscErrorCode PetscCDFConstant1D(const PetscReal[], const PetscReal[], PetscReal[]);
552 PETSC_EXTERN PetscErrorCode PetscPDFSampleConstant1D(const PetscReal[], const PetscReal[], PetscReal[]);
553 PETSC_EXTERN PetscErrorCode PetscPDFConstant2D(const PetscReal[], const PetscReal[], PetscReal[]);
554 PETSC_EXTERN PetscErrorCode PetscCDFConstant2D(const PetscReal[], const PetscReal[], PetscReal[]);
555 PETSC_EXTERN PetscErrorCode PetscPDFSampleConstant2D(const PetscReal[], const PetscReal[], PetscReal[]);
556 PETSC_EXTERN PetscErrorCode PetscPDFConstant3D(const PetscReal[], const PetscReal[], PetscReal[]);
557 PETSC_EXTERN PetscErrorCode PetscCDFConstant3D(const PetscReal[], const PetscReal[], PetscReal[]);
558 PETSC_EXTERN PetscErrorCode PetscPDFSampleConstant3D(const PetscReal[], const PetscReal[], PetscReal[]);
559 PETSC_EXTERN PetscErrorCode PetscProbCreateFromOptions(PetscInt, const char[], const char[], PetscProbFunc *, PetscProbFunc *, PetscProbFunc *);
560 
561 #include <petscvec.h>
562 
563 PETSC_EXTERN PetscErrorCode PetscProbComputeKSStatistic(Vec, PetscProbFunc, PetscReal *);
564 
565 #endif
566