From: Wolfgang Bangerth Date: Fri, 27 Mar 2020 03:41:37 +0000 (-0600) Subject: Small edits to the step-67.cc file. X-Git-Tag: v9.2.0-rc1~338^2~2^2~5 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6a43b5c0100be8893f75a9cdcabebd9be4d212a6;p=dealii.git Small edits to the step-67.cc file. --- diff --git a/examples/step-67/step-67.cc b/examples/step-67/step-67.cc index d680b40529..d2fb016927 100644 --- a/examples/step-67/step-67.cc +++ b/examples/step-67/step-67.cc @@ -50,9 +50,9 @@ #include #include -// This includes the CellwiseInverseMassMatrix data structure for the -// definition of the interface to mass matrix inversion, the only new include -// file for this tutorial program. +// The following file includes the CellwiseInverseMassMatrix data structure +// that we will use for the mass matrix inversion, the only new include +// file for this tutorial program: #include @@ -78,7 +78,8 @@ namespace Euler_DG constexpr unsigned int n_global_refinements = 3; constexpr unsigned int fe_degree = 5; constexpr unsigned int n_q_points_1d = fe_degree + 2; - using Number = double; + + using Number = double; constexpr double gamma = 1.4; constexpr double FINAL_TIME = testcase == 0 ? 10 : 2.0; @@ -119,7 +120,8 @@ namespace Euler_DG // We now define a class with the exact solution for the test case 0 and one // with a background flow field for test case 1 of the channel. Given that // the Euler equations are a problem with $d+2$ equations in $d$ dimensions, - // we need to select the function with the correct number of components. + // we need to tell the Function base class about the correct number of + // components. template class ExactSolution : public Function { @@ -144,12 +146,12 @@ namespace Euler_DG // some expression. Since `std::pow()` has pretty slow implementations on // some systems, we replace it by logarithm followed by exponentiation (of // base 2), which is mathematically equivalent but usually much better - // optimized. We note that this formula might lose accuracy in the last - // digits for very small numbers compared to `std::pow()`, we are happy with + // optimized. This formula might lose accuracy in the last digits + // for very small numbers compared to `std::pow()`, but we are happy with // it anyway, since small numbers map to data close to 1. // // For the channel test case, we simply select a density of 1, a velocity of - // 0.4 in x direction and zero in the other directions, and an energy that + // 0.4 in $x$ direction and zero in the other directions, and an energy that // corresponds to a speed of sound of 1.3 measured against the background // velocity field, computed from the relation $E = \frac{c^2}{\gamma (\gamma // -1)} + \frac 12 \rho \|u\|^2$. @@ -157,45 +159,56 @@ namespace Euler_DG double ExactSolution::value(const Point & x, const unsigned int component) const { - double t = this->get_time(); - if (testcase == 0) + const double t = this->get_time(); + + switch (testcase) { - Assert(dim == 2, ExcNotImplemented()); - double beta = 5; - Point x0; - x0[0] = 5.; - double radius_sqr = - (x - x0).norm_square() - 2. * (x[0] - x0[0]) * t + t * t; - double factor = beta / (numbers::PI * 2) * std::exp(1. - radius_sqr); - const double density_log = std::log2( - std::abs(1. - (gamma - 1.) / gamma * 0.25 * factor * factor)); - const double density = std::exp2(density_log * (1. / (gamma - 1.))); - const double u = 1. - factor * (x[1] - x0[1]); - const double v = factor * (x[0] - t - x0[0]); - if (component == 0) - return density; - else if (component == 1) - return density * u; - else if (component == 2) - return density * v; - else + case 0: { - const double pressure = - std::exp2(density_log * (gamma / (gamma - 1.))); - return pressure / (gamma - 1.) + - 0.5 * (density * u * u + density * v * v); + Assert(dim == 2, ExcNotImplemented()); + const double beta = 5; + + Point x0; + x0[0] = 5.; + const double radius_sqr = + (x - x0).norm_square() - 2. * (x[0] - x0[0]) * t + t * t; + const double factor = + beta / (numbers::PI * 2) * std::exp(1. - radius_sqr); + const double density_log = std::log2( + std::abs(1. - (gamma - 1.) / gamma * 0.25 * factor * factor)); + const double density = std::exp2(density_log * (1. / (gamma - 1.))); + const double u = 1. - factor * (x[1] - x0[1]); + const double v = factor * (x[0] - t - x0[0]); + + if (component == 0) + return density; + else if (component == 1) + return density * u; + else if (component == 2) + return density * v; + else + { + const double pressure = + std::exp2(density_log * (gamma / (gamma - 1.))); + return pressure / (gamma - 1.) + + 0.5 * (density * u * u + density * v * v); + } } - } - else - { - if (component == 0) - return 1.; - else if (component == 1) - return 0.4; - else if (component == dim + 1) - return 3.097857142857143; - else - return 0.; + + case 1: + { + if (component == 0) + return 1.; + else if (component == 1) + return 0.4; + else if (component == dim + 1) + return 3.097857142857143; + else + return 0.; + } + + default: + Assert(false, ExcNotImplemented()); } } @@ -204,7 +217,7 @@ namespace Euler_DG // @sect3{Low-storage explicit Runge--Kutta time integrators} // The next few lines implement a few low-storage variants of Runge--Kutta - // methods. These methods have specific Butcher tableaus with coefficients + // methods. These methods have specific Butcher tableaux with coefficients // $b_i$ and $a_i$ as shown in the introduction. As usual in Runge--Kutta // method, we can deduce time steps, $c_i = \sum_{j=1}^{i-2} b_i + a_{i-1}$ // from those coefficients. The main advantage of this kind of scheme is the @@ -236,84 +249,100 @@ namespace Euler_DG public: LowStorageRungeKuttaIntegrator(const LowStorageRungeKuttaScheme scheme) { - // First comes the three-stage scheme of order three by Kennedy et al + // First comes the three-stage scheme of order three by Kennedy et al. // (2000). While its stability region is significantly smaller than for // the other schemes, it only involves three stages, so it is very // competitive in terms of the work per stage. - if (scheme == stage_3_order_3) - { - bi = {{0.245170287303492, 0.184896052186740, 0.569933660509768}}; - ai = {{0.755726351946097, 0.386954477304099}}; - } - // The next scheme is a five-stage scheme of order four, again defined - // in the paper by Kennedy et al. (2000). - else if (scheme == stage_5_order_4) - { - bi = {{1153189308089. / 22510343858157., - 1772645290293. / 4653164025191., - -1672844663538. / 4480602732383., - 2114624349019. / 3568978502595., - 5198255086312. / 14908931495163.}}; - ai = {{970286171893. / 4311952581923., - 6584761158862. / 12103376702013., - 2251764453980. / 15575788980749., - 26877169314380. / 34165994151039.}}; - } - // This scheme of seven stages and order four has been explicitly - // derived for acoustics problems. It is a balance of accuracy for - // imaginary eigenvalues among fourth order schemes, combined with a - // large stability region. Since DG schemes are dissipative among the - // highest frequencies, this does not necessarily translate to the - // highest possible time step per stage. In the context of the present - // tutorial program, the numerical flux plays a crucial role in the - // disspiation and thus also the maximal stable time step size. For the - // modified Lax--Friedrichs flux, this scheme is similar to the - // `stage_5_order_4` scheme in terms of step size per stage if only - // stability is considered, but somewhat less efficient for the HLL - // flux. - else if (scheme == stage_7_order_4) - { - bi = {{0.0941840925477795334, - 0.149683694803496998, - 0.285204742060440058, - -0.122201846148053668, - 0.0605151571191401122, - 0.345986987898399296, - 0.186627171718797670}}; - ai = {{0.241566650129646868 + bi[0], - 0.0423866513027719953 + bi[1], - 0.215602732678803776 + bi[2], - 0.232328007537583987 + bi[3], - 0.256223412574146438 + bi[4], - 0.0978694102142697230 + bi[5]}}; - } - // The last scheme included here is the nine-stage scheme of order five - // from Kennedy et al. (2000). It is the most accurate among the schemes - // used here, but the higher order of accuracy sacrifices some - // stability, so the step length normalized per stage is less than for - // the fourth order schemes. - else if (scheme == stage_9_order_5) + switch (scheme) { - bi = {{2274579626619. / 23610510767302., - 693987741272. / 12394497460941., - -347131529483. / 15096185902911., - 1144057200723. / 32081666971178., - 1562491064753. / 11797114684756., - 13113619727965. / 44346030145118., - 393957816125. / 7825732611452., - 720647959663. / 6565743875477., - 3559252274877. / 14424734981077.}}; - ai = {{1107026461565. / 5417078080134., - 38141181049399. / 41724347789894., - 493273079041. / 11940823631197., - 1851571280403. / 6147804934346., - 11782306865191. / 62590030070788., - 9452544825720. / 13648368537481., - 4435885630781. / 26285702406235., - 2357909744247. / 11371140753790.}}; + case stage_3_order_3: + { + bi = {{0.245170287303492, 0.184896052186740, 0.569933660509768}}; + ai = {{0.755726351946097, 0.386954477304099}}; + + break; + } + + // The next scheme is a five-stage scheme of order four, again + // defined in the paper by Kennedy et al. (2000). + case stage_5_order_4: + { + bi = {{1153189308089. / 22510343858157., + 1772645290293. / 4653164025191., + -1672844663538. / 4480602732383., + 2114624349019. / 3568978502595., + 5198255086312. / 14908931495163.}}; + ai = {{970286171893. / 4311952581923., + 6584761158862. / 12103376702013., + 2251764453980. / 15575788980749., + 26877169314380. / 34165994151039.}}; + + break; + } + + // The following scheme of seven stages and order four has been + // explicitly derived for acoustics problems. It is a balance of + // accuracy for imaginary eigenvalues among fourth order schemes, + // combined with a large stability region. Since DG schemes are + // dissipative among the highest frequencies, this does not + // necessarily translate to the highest possible time step per + // stage. In the context of the present tutorial program, the + // numerical flux plays a crucial role in the dissipation and thus + // also the maximal stable time step size. For the modified + // Lax--Friedrichs flux, this scheme is similar to the + // `stage_5_order_4` scheme in terms of step size per stage if only + // stability is considered, but somewhat less efficient for the HLL + // flux. + case stage_7_order_4: + { + bi = {{0.0941840925477795334, + 0.149683694803496998, + 0.285204742060440058, + -0.122201846148053668, + 0.0605151571191401122, + 0.345986987898399296, + 0.186627171718797670}}; + ai = {{0.241566650129646868 + bi[0], + 0.0423866513027719953 + bi[1], + 0.215602732678803776 + bi[2], + 0.232328007537583987 + bi[3], + 0.256223412574146438 + bi[4], + 0.0978694102142697230 + bi[5]}}; + + break; + } + + // The last scheme included here is the nine-stage scheme of order + // five from Kennedy et al. (2000). It is the most accurate among + // the schemes used here, but the higher order of accuracy + // sacrifices some stability, so the step length normalized per + // stage is less than for the fourth order schemes. + case stage_9_order_5: + { + bi = {{2274579626619. / 23610510767302., + 693987741272. / 12394497460941., + -347131529483. / 15096185902911., + 1144057200723. / 32081666971178., + 1562491064753. / 11797114684756., + 13113619727965. / 44346030145118., + 393957816125. / 7825732611452., + 720647959663. / 6565743875477., + 3559252274877. / 14424734981077.}}; + ai = {{1107026461565. / 5417078080134., + 38141181049399. / 41724347789894., + 493273079041. / 11940823631197., + 1851571280403. / 6147804934346., + 11782306865191. / 62590030070788., + 9452544825720. / 13648368537481., + 4435885630781. / 26285702406235., + 2357909744247. / 11371140753790.}}; + + break; + } + + default: + AssertThrow(false, ExcNotImplemented()); } - else - AssertThrow(false, ExcNotImplemented()); } unsigned int n_stages() const @@ -330,7 +359,7 @@ namespace Euler_DG // to delegate the vectors and coefficients. // // We separately call the operator for the first stage because we need - // slightly modified arguments there: Here, we evaluate the solution from + // slightly modified arguments there: We evaluate the solution from // the old solution $\mathbf{w}^n$ rather than a $\mathbf r_i$ vector, so // the first argument is `solution`. We here let the stage vector // $\mathbf{r}_i$ also hold the temporary result of the evaluation, as it @@ -348,6 +377,7 @@ namespace Euler_DG VectorType & vec_ki) { AssertDimension(ai.size() + 1, bi.size()); + pde_operator.perform_stage(current_time, bi[0] * time_step, ai[0] * time_step,