From: Wolfgang Bangerth Date: Wed, 22 Mar 2000 14:01:32 +0000 (+0000) Subject: Finish (I guess). X-Git-Tag: v8.0.0~20764 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f5117c62809eeff7868a9a5e7aa16873de1ed7b0;p=dealii.git Finish (I guess). git-svn-id: https://svn.dealii.org/trunk@2611 0785d39b-7218-0410-832d-ea1e28bc413d --- diff --git a/deal.II/examples/step-7/step-7.cc b/deal.II/examples/step-7/step-7.cc index 97b283dfd1..cd7837109b 100644 --- a/deal.II/examples/step-7/step-7.cc +++ b/deal.II/examples/step-7/step-7.cc @@ -62,6 +62,13 @@ // ``FEValues'' class: #include + // We need one more include from + // standard C++, which is necessary + // when we try to find out the actual + // type behind a pointer to a base + // class. We will explain this in + // slightly more detail below. +#include #include @@ -317,32 +324,66 @@ double RightHandSide::value (const Point &p, // Then we need the class that does - // all the work. -//....................... + // all the work. It is mostly the + // same as in previous examples, and + // we will discuss the differences + // only when we declare the + // respective functions or variables + // below. template class LaplaceProblem { public: -//......... + // We will use this class in + // several modes: for different + // finite elements, as well as + // for adaptive and global + // refinement. The decision + // whether global or adaptive + // refinement shall be used is + // communicated to the + // constructor of this class + // through an enumeration type, + // which we declare here: enum RefinementMode { global_refinement, adaptive_refinement }; -//....... + // This is the constructor of the + // class, it takes the finite + // element and the refinement + // mode as parameter and stores + // them in local variables. LaplaceProblem (const FiniteElement &fe, const RefinementMode refinement_mode); + + // The following two functions + // are the same as in previous + // examples. ~LaplaceProblem (); void run (); private: -//....... + // As are these: void setup_system (); void assemble_system (); void solve (); void refine_grid (); + + // After the solution has been + // computed, we perform some + // analysis on it, such as + // computing the error in various + // norms. This is done in the + // following function. To enable + // some output, we pass it the + // number of the refinement + // cycle. void process_solution (const unsigned int cycle); + // Now for the data elements of + // this class: Triangulation triangulation; DoFHandler dof_handler; @@ -536,8 +577,19 @@ class LaplaceProblem Vector solution; Vector system_rhs; -//............. - RefinementMode refinement_mode; + + // The second last variable + // stores the refinement mode + // passed to the + // constructor. Since it is only + // set in the constructor, we can + // declare this variable + // constant, to avoid that + // someone sets it involuntarily + // (e.g. in an `if'-statement + // where == was written as = by + // chance). + const RefinementMode refinement_mode; // For each refinement level some // important data (like the @@ -560,7 +612,12 @@ class LaplaceProblem -//........ + // In the constructor of this class, + // we only set the variables passed + // to this object, and associate the + // DoF handler object with the + // triangulation (which is empty at + // present, however). template LaplaceProblem::LaplaceProblem (const FiniteElement &fe, const RefinementMode refinement_mode) : @@ -982,18 +1039,44 @@ void LaplaceProblem::solve () }; -//..................... + // Now for the function doing grid + // refinement. Depending on the + // refinement mode passed to the + // constructor, we do global or + // adaptive refinement. template void LaplaceProblem::refine_grid () { switch (refinement_mode) { + // If global refinement is + // required, this is simple: case global_refinement: { triangulation.refine_global (1); break; }; - + + // In case of adaptive + // refinement, we use the same + // functions and classes as in + // the previous example + // program. Note that one + // could treat Neumann + // boundaries differently than + // Dirichlet boundaries, and + // one should in fact do so + // here since we have Neumann + // boundary conditions on part + // of the boundaries, but + // since we don't have a + // function here that + // describes the Neumann + // values (we only construct + // these values from the exact + // solution when assembling + // the matrix), we omit this + // detail here. case adaptive_refinement: { Vector estimated_error_per_cell (triangulation.n_active_cells()); @@ -1015,20 +1098,70 @@ void LaplaceProblem::refine_grid () }; }; -//............... + + + // Finally process the solution after + // it has been computed. For this, we + // integrate the error in various + // norms, and we generate tables that + // will be later used to display the + // convergence against the continuous + // solution in a nice format. template void LaplaceProblem::process_solution (const unsigned int cycle) { + // In order to integrate the + // difference between computed + // numerical solution and the + // continuous solution (described + // by the ``Solution'' class + // defined at the top of this + // file), we first need a vector + // that will hold the norm of the + // error on each cell. Since + // accuracy with 16 digits is not + // so important for these + // quantities, we sace some memory + // by using ``float'' instead of + // ``double'' values. Vector difference_per_cell (triangulation.n_active_cells()); - + + // Next we use a function from the + // library which computes the error + // in the L2 norm on each cell. We + // have to pass it the DoF handler + // object, the vector holding the + // nodal values of the numerical + // solution, the continuous + // solution as a function object, + // the vector into which it shall + // place the norm of the error on + // each cell, a quadrature rule by + // which this norm shall be + // computed, and the type of norm + // to be used. Here, we use a Gauss + // formula with three points in + // each space direction, and + // compute the L2 norm. VectorTools::integrate_difference (dof_handler, solution, Solution(), difference_per_cell, QGauss3(), L2_norm); + // Finally, we want to get the + // global L2 norm. This can of + // course be obtained by summing + // the squares of the norms on each + // cell, and taking the square root + // of that value. This is + // equivalent to taking the l2 + // (lower case ``l'') norm of the + // vector of norms on each cell: const double L2_error = difference_per_cell.l2_norm(); + // The same procedure is done to + // get the H1 semi-norm: VectorTools::integrate_difference (dof_handler, solution, Solution(), @@ -1037,14 +1170,48 @@ void LaplaceProblem::process_solution (const unsigned int cycle) H1_seminorm); const double H1_error = difference_per_cell.l2_norm(); + // Finally, we compute the maximum + // norm. Of course, we can't + // actually use the true maximum, + // but only the maximum at the + // quadrature points. Since this + // quite sensitively depends on the + // quadrature rule being used, and + // since we would like to avoid + // false results due to + // super-convergence effects at + // some points, we use a special + // quadrature rule that is obtained + // by iterating the trapezoidal + // rule five times in each space + // direction. Note that the + // constructor of the ``QIterated'' + // class takes a one-dimensional + // quadrature rule and a number + // that tells it how often it shall + // use this rule in each space + // direction. + QTrapez<1> q_trapez; + QIterated q_iterated (q_trapez, 5); + + // Using this special quadrature + // rule, we can now try to find the + // maximal error on each cell: VectorTools::integrate_difference (dof_handler, solution, Solution(), difference_per_cell, - QGauss3(), + q_iterated, Linfty_norm); + // Obviously, the maximal error + // globally is the maximum over the + // maximal errors on each cell: const double Linfty_error = difference_per_cell.linfty_norm(); + // After all these errors have been + // computed, we finally write some + // output and put all the data into + // a table. const unsigned int n_active_cells=triangulation.n_active_cells(); const unsigned int n_dofs=dof_handler.n_dofs(); @@ -1128,7 +1295,7 @@ void LaplaceProblem::process_solution (const unsigned int cycle) template void LaplaceProblem::run () { - for (unsigned int cycle=0; cycle<6; ++cycle) + for (unsigned int cycle=0; cycle<7; ++cycle) { // The first action in each // iteration of the outer loop @@ -1217,14 +1384,17 @@ void LaplaceProblem::run () cell->face(face)->set_boundary_indicator (1); } else - // If this is not the first - // step, the we call - // ``refine_grid'' to - // actually refine the grid - // according to the - // refinement mode passed to - // the constructor. - refine_grid (); + { + // If this is not the first + // step, the we call + // ``refine_grid'' to + // actually refine the grid + // according to the + // refinement mode passed to + // the constructor. + refine_grid (); + }; + // The next steps you already // know from previous @@ -1269,6 +1439,40 @@ void LaplaceProblem::run () default: Assert (false, ExcInternalError()); }; + + // We augment the filename by a + // postfix denoting the finite + // element which we have used in + // the computation. Finding out + // which finite element we are + // actually using is not that + // simple here, since we only have + // a pointer to the common base + // class of all finite elements, + // but we can use a rather new + // feature of C++ to check whether + // the actual type of the object + // pointed to by ``fe'' is an + // ``FEQ1'', ``FEQ2'', or something + // different. + if (typeid(*fe)==typeid(const FEQ1)) + filename += "-q1"; + else + if (typeid(*fe)==typeid(const FEQ2)) + filename += "-q2"; + else + // The finite element is + // neither Q1 nor Q2. This + // should not have happened, + // but maybe someone has tried + // to change this in ``main'', + // so it might happen. We catch + // this case and throw an + // exception, since we don't + // know how to name the + // respective output file + Assert (false, ExcInternalError()); + filename += ".gmv"; ofstream output (filename.c_str()); @@ -1277,7 +1481,70 @@ void LaplaceProblem::run () DataOut data_out; data_out.attach_dof_handler (dof_handler); data_out.add_data_vector (solution, "solution"); - data_out.build_patches (); + + // Now building the intermediate + // format as before is the next + // step. We introduce one more + // feature of deal.II here. The + // background is the following: in + // some of the runs of this + // function, we have used + // biquadratic finite + // elements. However, since almost + // all output formats only support + // bilinear data, the data is + // written only bilinear, and + // information is lost + // therefore. Of course, we can't + // change the format in which + // graphic programs accept their + // inputs, but we can write the + // data differently such that we + // more closely resemble the + // information available in the + // quadratic approximation. We can, + // for example, write each cell as + // four subcells with bilinear data + // each, such that we have nine + // data points for each cell in the + // triangulation. The graphic + // programs will, of course, + // display this data still only + // bilinear, but at least we have + // given some more of the + // information we have. + // + // In order to allow writing more + // than one subcell per actual + // cell, the ``build_patches'' + // function accepts a parameter + // (the default is ``1'', which is + // why you haven't seen this + // parameter in previous + // examples). This parameter + // denotes into how many subcells + // per space direction each cell + // shall be subdivided for + // output. For example, if you give + // ``2'', this leads to 4 cells in + // 2D and 8 cells in 3D. For + // quadratic elements, two subcells + // per space direction is obviously + // the right choice, so this is + // what we choose: + unsigned int n_subcells; + if (typeid(*fe) == typeid(const FEQ1)) + n_subcells = 1; + else + if (typeid(*fe) == typeid(const FEQ2)) + n_subcells = 2; + else + Assert (false, ExcInternalError()); + + data_out.build_patches (n_subcells); + + // Finally write out the data in + // GMV format. data_out.write_gmv (output); // In each cycle values were added to @@ -1287,14 +1554,39 @@ void LaplaceProblem::run () // and the captions may not be printed // directly above the specific columns. convergence_table.write_text(cout); - // The table can also be written into a tex file. - // The (nicely) formatted table - // can be viewed at after - // calling `latex whole_table' and - // e.g. `xdvi whole_table'. + // The table can also be written + // into a tex file. The (nicely) + // formatted table can be viewed at + // after calling `latex filename' + // and e.g. `xdvi filename', where + // filename is the name of the file + // which we construct from the name + // of the finite element and the + // refinement mode, as above if (true) { - ofstream table_file("whole_table.tex"); + string filename = "error"; + switch (refinement_mode) + { + case global_refinement: + filename += "-global"; + break; + case adaptive_refinement: + filename += "-adaptive"; + break; + default: + Assert (false, ExcInternalError()); + }; + if (typeid(*fe)==typeid(const FEQ1)) + filename += "-q1"; + else + if (typeid(*fe)==typeid(const FEQ2)) + filename += "-q2"; + else + Assert (false, ExcInternalError()); + filename += ".tex"; + + ofstream table_file(filename.c_str()); convergence_table.write_tex(table_file); table_file.close(); } @@ -1363,29 +1655,99 @@ void LaplaceProblem::run () } // Finally, the convergence chart - // is written: + // is written. The filename is + // again constructed as above. convergence_table.write_text(cout); if (true) { - ofstream table_file("convergence_table.tex"); + string filename = "convergence"; + switch (refinement_mode) + { + case global_refinement: + filename += "-global"; + break; + case adaptive_refinement: + filename += "-adaptive"; + break; + default: + Assert (false, ExcInternalError()); + }; + if (typeid(*fe)==typeid(const FEQ1)) + filename += "-q1"; + else + if (typeid(*fe)==typeid(const FEQ2)) + filename += "-q2"; + else + Assert (false, ExcInternalError()); + filename += ".tex"; + + ofstream table_file(filename.c_str()); convergence_table.write_tex(table_file); table_file.close(); } }; -//................. + // The main function is mostly as + // before. The only difference is + // that we solve three times, once + // for Q1 and adaptive refinement, + // once for Q1 elements and global + // refinement, and once for Q2 + // elements and global refinement. int main () { try { deallog.depth_console (0); - FEQ1<2> fe; -// LaplaceProblem<2> laplace_problem_2d (fe, LaplaceProblem<2>::adaptive_refinement); - LaplaceProblem<2> laplace_problem_2d (fe, LaplaceProblem<2>::global_refinement); - laplace_problem_2d.run (); + // Now for the three calls to + // the main class. Each call is + // blocked into curly braces in + // order to detroy the + // respective objects (i.e. the + // finite element and the + // LaplaceProblem object) at + // the end of the block and + // before we go to the next + // run. + { + cout << "Solving with Q1 elements, adaptive refinement" << endl + << "=============================================" << endl + << endl; + + FEQ1<2> fe; + LaplaceProblem<2> laplace_problem_2d (fe, LaplaceProblem<2>::adaptive_refinement); + laplace_problem_2d.run (); + + cout << endl; + }; + + { + cout << "Solving with Q1 elements, global refinement" << endl + << "===========================================" << endl + << endl; + + FEQ1<2> fe; + LaplaceProblem<2> laplace_problem_2d (fe, LaplaceProblem<2>::global_refinement); + laplace_problem_2d.run (); + + cout << endl; + }; + + { + cout << "Solving with Q2 elements, global refinement" << endl + << "===========================================" << endl + << endl; + + FEQ2<2> fe; + LaplaceProblem<2> laplace_problem_2d (fe, LaplaceProblem<2>::global_refinement); + laplace_problem_2d.run (); + + cout << endl; + }; + } catch (exception &exc) {