From: Wolfgang Bangerth Date: Wed, 11 Nov 2015 21:23:13 +0000 (-0600) Subject: Document FiniteElement::get_*_data(). X-Git-Tag: v8.4.0-rc2~220^2 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F1863%2Fhead;p=dealii.git Document FiniteElement::get_*_data(). --- diff --git a/include/deal.II/fe/fe.h b/include/deal.II/fe/fe.h index 4fd17ef699..7cd398fea2 100644 --- a/include/deal.II/fe/fe.h +++ b/include/deal.II/fe/fe.h @@ -2193,14 +2193,81 @@ protected: requires_update_flags (const UpdateFlags update_flags) const = 0; /** - * Prepare internal data structures and fill in values independent of the - * cell. Return a pointer to an object of which the caller of this function - * then has to assume ownership (which includes destruction when it is no - * more needed). + * Create an internal data object and return a pointer to it of which the + * caller of this function then assumes ownership. This object will + * then be passed to the FiniteElement::fill_fe_values() every time + * the finite element shape functions and their derivatives are evaluated + * on a concrete cell. The object created here is therefore used by + * derived classes as a place for scratch objects that are used in + * evaluating shape functions, as well as to store information that + * can be pre-computed once and re-used on every cell (e.g., for + * evaluating the values and gradients of shape functions on the + * reference cell, for later re-use when transforming these values to + * a concrete cell). + * + * This function is the first one called in the process of initializing + * a FEValues object for a given mapping and finite element object. The + * returned object will later be passed to FiniteElement::fill_fe_values() + * for a concrete cell, which will itself place its output into an object + * of type internal::FEValues::FiniteElementRelatedData. Since there may + * be data that can already be computed in its final form on the + * reference cell, this function also receives a reference to the + * internal::FEValues::FiniteElementRelatedData object as its last argument. + * This output argument is guaranteed to always be the same one when used + * with the InternalDataBase object returned by this function. In other + * words, the subdivision of scratch data and final data in the returned + * object and the @p output_data object is as follows: If data can be + * pre-computed on the reference cell in the exact form in which it + * will later be needed on a concrete cell, then this function should + * already emplace it in the @p output_data object. An example are the + * values of shape functions at quadrature points for the usual + * Lagrange elements which on a concrete cell are identical to the + * ones on the reference cell. On the other hand, if some data can + * be pre-computed to make computations on a concrete cell cheaper, + * then it should be put into the returned object for later re-use + * in a derive class's implementation of FiniteElement::fill_fe_values(). + * An example are the gradients of shape functions on the reference + * cell for Lagrange elements: to compute the gradients of the shape + * functions on a concrete cell, one has to multiply the gradients on + * the reference cell by the inverse of the Jacobian of the mapping; + * consequently, we cannot already compute the gradients on a concrete + * cell at the time the current function is called, but we can at least + * pre-compute the gradients on the reference cell, and store it + * in the object returned. * * An extensive discussion of the interaction between this function and * FEValues can be found in the @ref FE_vs_Mapping_vs_FEValues documentation - * module. + * module. See also the documentation of the InternalDataBase class. + * + * @param[in] update_flags A set of UpdateFlags values that describe + * what kind of information the FEValues object requests the finite + * element to compute. This set of flags may also include information + * that the finite element can not compute, e.g., flags that pertain + * to data produced by the mapping. An implementation of this function + * needs to set up all data fields in the returned object that are + * necessary to produce the finite-element related data specified by + * these flags, and may already pre-compute part of this information + * as discussed above. Elements may want to store these update flags + * (or a subset of these flags) in InternalDataBase::update_each so + * they know at the time when FinitElement::fill_fe_values() is called + * what they are supposed to compute + * @param[in] mapping A reference to the mapping used for computing + * values and derivatives of shape functions. + * @param[in] quadrature A reference to the object that describes where + * the shape functions should be evaluated. + * @param[out] output_data A reference to the object that FEValues + * will use in conjunction with the object returned here and where + * an implementation of FiniteElement::fill_fe_values() will place + * the requested information. This allows the current function + * to already pre-compute pieces of information that can be computed + * on the reference cell, as discussed above. FEValues guarantees + * that this output object and the object returned by the current + * function will always be used together. + * @return A pointer to an object of a type derived from InternalDataBase + * and that derived classes can use to store scratch data that can + * be pre-computed, or for scratch arrays that then only need to + * be allocated once. The calling site assumes ownership of this + * object and will delete it when it is no longer necessary. */ virtual InternalDataBase * @@ -2210,19 +2277,46 @@ protected: dealii::internal::FEValues::FiniteElementRelatedData &output_data) const = 0; /** - * Prepare internal data structure for transformation of faces and fill in - * values independent of the cell. Return a pointer to an object of which - * the caller of this function then has to assume ownership (which includes - * destruction when it is no more needed). + * Like get_data(), but return an object that will later be used for + * evaluating shape function information at quadrature points on faces + * of cells. The object will then be used in calls to implementations of + * FiniteElement::fill_fe_face_values(). See the documentation of get_data() + * for more information. * * The default implementation of this function converts the face quadrature * into a cell quadrature with appropriate quadrature point locations, * and with that calls the get_data() function above that has to be * implemented in derived classes. * - * An extensive discussion of the interaction between this function and - * FEValues can be found in the @ref FE_vs_Mapping_vs_FEValues documentation - * module. + * @param[in] update_flags A set of UpdateFlags values that describe + * what kind of information the FEValues object requests the finite + * element to compute. This set of flags may also include information + * that the finite element can not compute, e.g., flags that pertain + * to data produced by the mapping. An implementation of this function + * needs to set up all data fields in the returned object that are + * necessary to produce the finite-element related data specified by + * these flags, and may already pre-compute part of this information + * as discussed above. Elements may want to store these update flags + * (or a subset of these flags) in InternalDataBase::update_each so + * they know at the time when FinitElement::fill_fe_face_values() is called + * what they are supposed to compute + * @param[in] mapping A reference to the mapping used for computing + * values and derivatives of shape functions. + * @param[in] quadrature A reference to the object that describes where + * the shape functions should be evaluated. + * @param[out] output_data A reference to the object that FEValues + * will use in conjunction with the object returned here and where + * an implementation of FiniteElement::fill_fe_face_values() will place + * the requested information. This allows the current function + * to already pre-compute pieces of information that can be computed + * on the reference cell, as discussed above. FEValues guarantees + * that this output object and the object returned by the current + * function will always be used together. + * @return A pointer to an object of a type derived from InternalDataBase + * and that derived classes can use to store scratch data that can + * be pre-computed, or for scratch arrays that then only need to + * be allocated once. The calling site assumes ownership of this + * object and will delete it when it is no longer necessary. */ virtual InternalDataBase * @@ -2232,19 +2326,46 @@ protected: dealii::internal::FEValues::FiniteElementRelatedData &output_data) const; /** - * Prepare internal data structure for transformation of children of faces - * and fill in values independent of the cell. Return a pointer to an - * object of which the caller of this function then has to assume ownership - * (which includes destruction when it is no more needed). + * Like get_data(), but return an object that will later be used for + * evaluating shape function information at quadrature points on children + * of faces of cells. The object will then be used in calls to + * implementations of FiniteElement::fill_fe_subface_values(). See the + * documentation of get_data() for more information. * * The default implementation of this function converts the face quadrature * into a cell quadrature with appropriate quadrature point locations, * and with that calls the get_data() function above that has to be * implemented in derived classes. * - * An extensive discussion of the interaction between this function and - * FEValues can be found in the @ref FE_vs_Mapping_vs_FEValues documentation - * module. + * @param[in] update_flags A set of UpdateFlags values that describe + * what kind of information the FEValues object requests the finite + * element to compute. This set of flags may also include information + * that the finite element can not compute, e.g., flags that pertain + * to data produced by the mapping. An implementation of this function + * needs to set up all data fields in the returned object that are + * necessary to produce the finite-element related data specified by + * these flags, and may already pre-compute part of this information + * as discussed above. Elements may want to store these update flags + * (or a subset of these flags) in InternalDataBase::update_each so + * they know at the time when FinitElement::fill_fe_subface_values() + * is called what they are supposed to compute + * @param[in] mapping A reference to the mapping used for computing + * values and derivatives of shape functions. + * @param[in] quadrature A reference to the object that describes where + * the shape functions should be evaluated. + * @param[out] output_data A reference to the object that FEValues + * will use in conjunction with the object returned here and where + * an implementation of FiniteElement::fill_fe_subface_values() will place + * the requested information. This allows the current function + * to already pre-compute pieces of information that can be computed + * on the reference cell, as discussed above. FEValues guarantees + * that this output object and the object returned by the current + * function will always be used together. + * @return A pointer to an object of a type derived from InternalDataBase + * and that derived classes can use to store scratch data that can + * be pre-computed, or for scratch arrays that then only need to + * be allocated once. The calling site assumes ownership of this + * object and will delete it when it is no longer necessary. */ virtual InternalDataBase *