... 19. Partial Differential Equations 19.0 IntroductionThe numerical treatment ofpartialdifferentialequations is, by itself, a vastsubject. Partialdifferentialequations are at the heart of ... are the variables?• What equations are satisfied in the interior of the region of interest?• What equations are satisfied by points on the boundary of the region of interest? (Here Dirichlet ... entiresecondvolume of Numerical Recipes dealing with partialdifferentialequations alone. (Thereferences[1-4]provide, of course, available alternatives.) In most mathematics books, partialdifferential equations...
... various ways of improving the accuracy of first-order upwinddifferencing. In the continuum equation, material originally a distance v∆t away840Chapter 19. PartialDifferential Equations Sample ... own domain of dependency determined by the choice of points on one time slice (shown as connected solid dots) whose values are used in determining a newpoint (shown connected by dashed lines). ... viscosity to the equations, modeling the way Nature uses real viscosityto smooth discontinuities. A good starting point for trying out this method is thedifferencing scheme in §12.11 of [1]. This...
... America).Chapter 16. Integration of Ordinary Differential Equations 16.0 IntroductionProblems involving ordinary differentialequations (ODEs) can always bereduced to the study of sets of first-order differential ... description of each of these types follows.1. Runge-Kutta methods propagate a solution over an interval by combiningthe information from several Euler-style steps (each involving one evaluation of theright-hand ... 1973,Computational Methods in Ordinary Differential Equations (New York: Wiley).Lapidus, L., and Seinfeld, J. 1971,Numerical Solution of Ordinary Differential Equations (NewYork: Academic...
... discussion of the pitfalls in constructing a good Runge-Kutta code is given in [3].Here is the routine for carrying out one classical Runge-Kutta step on a set of n differential equations. You input ... 1973,Computational Methods in Ordinary Differential Equations (New York: Wiley).Lapidus, L., and Seinfeld, J. 1971,Numerical Solution of Ordinary Differential Equations (NewYork: Academic ... the use of a step like (16.1.1) to take a “trial” step to themidpoint of the interval. Then use the value of both x and y at that midpointto compute the real step across the whole interval....
... evolution of the larger-scale features of interest takes place superposed with a kind of “frozen in (though fluctuating)background of small-scale stuff. This answer gives a differencing scheme ... form again and in practice usually retainsthe stability advantages of fully implicit differencing.Schr¨odinger EquationSometimes the physical problem being solved imposes constraints on ... evolve through of order λ2/(∆x)2steps before things start to happen on thescale of interest. This number of steps is usually prohibitive. We must thereforefind a stable way of taking timesteps...
... underlying PDEs, perhaps allowing second-orderspatial differencing for first-order -in- space PDEs. When you increase the order of a differencing method to greater than the order of the original ... Recipes Software. Permission is granted for internet users to make one paper copy for their own personal use. Further reproduction, or any copying of machine-readable files (including this ... America).are using is known to be extremely stable, we do not recommend anything higherthan second-order in time (for sets of first-order equations) . For spatial differencing,we recommend the order of the...
... level of CR, we have reduced the number ofequations by a factor of two. Since the resulting equations are of the same form as the original equation, wecan repeat the process. Taking the number of ... y-values on thesex-lines. Then fill in the intermediate x-lines as in the original CR algorithm.The trick is to choose the number of levels of CR so as to minimize the totalnumber of arithmetic operations. ... mentioned in §19.0, relaxation methods involve splitting the sparsematrix that arises from finite differencing and then iterating until a solution is found.There is another way of thinking about...
... y-values on thesex-lines. Then fill in the intermediate x-lines as in the original CR algorithm.The trick is to choose the number of levels of CR so as to minimize the totalnumber of arithmetic operations. ... N grid points in O(N ) operations.The “rapid” direct elliptic solvers discussed in §19.4 solve special kinds of elliptic equations in O(N log N) operations. The numerical coefficients in these ... the version of SOR implemented below, we shall adopt odd-even ordering.The last practical point is that in practice the asymptotic rate of convergence in SOR is not attained until of order J...
... methods.free_vector(ytemp,1,n);free_vector(ak6,1,n);free_vector(ak5,1,n);free_vector(ak4,1,n);free_vector(ak3,1,n);free_vector(ak2,1,n);}Noting that the above routines are all in single precision, don’t be too greedy in specifying eps. Thepunishment forexcessive greediness is interestingand worthyofGilbertand Sullivan’sMikado: ... North America).including garden-variety ODEs or sets of ODEs, and definite integrals (augmentingthe methods of Chapter 4). For storage of intermediate results (if you desire toinspect them) we ... + H, zn)](16.3.2)714Chapter 16. Integration of Ordinary Differential Equations Sample page from NUMERICAL RECIPES IN C: THE ART OF SCIENTIFIC COMPUTING (ISBN 0-521-43108-5)Copyright (C)...
... 722Chapter 16. Integration of Ordinary Differential Equations Sample page from NUMERICAL RECIPES IN C: THE ART OF SCIENTIFIC COMPUTING (ISBN 0-521-43108-5)Copyright (C) ... hmin) nrerror("Step size too small in odeint");h=hnext;}nrerror("Too many steps in routine odeint");}CITED REFERENCES AND FURTHER READING:Gear, C.W. 1971,Numerical Initial ... step h instead of the two required by second-order Runge-Kutta. Perhaps thereare applications where the simplicity of (16.3.2), easily coded in- line in some otherprogram, recommends it. In general,...
... remind you once again that scaling of the variables is often crucial forsuccessful integration ofdifferential equations. The scaling “trick” suggested in the discussion following equation (16.2.8) ... extrapolate eachcomponent of a vector of quantities.728Chapter 16. Integration of Ordinary Differential Equations Sample page from NUMERICAL RECIPES IN C: THE ART OF SCIENTIFIC COMPUTING (ISBN 0-521-43108-5)Copyright ... encountered in practice, is discussed in §16.7.)726Chapter 16. Integration of Ordinary Differential Equations Sample page from NUMERICAL RECIPES IN C: THE ART OF SCIENTIFIC COMPUTING (ISBN 0-521-43108-5)Copyright...
... isa particular class ofequations that occurs quite frequently in practice where you can gainabout a factor of two in efficiency by differencing the equations directly. The equations aresecond-order ... 734Chapter 16. Integration of Ordinary Differential Equations Sample page from NUMERICAL RECIPES IN C: THE ART OF SCIENTIFIC COMPUTING (ISBN 0-521-43108-5)Copyright (C) ... the arrays y and d2y are of length 2n for asystem of n second-order equations. The values of y arestoredinthefirstnelements of y,while the first derivatives are stored in the second n elements....
... as in the original Bulirsch-Stoer method.The starting point is an implicit form of the midpoint rule:yn+1− yn−1=2hfyn+1+ yn−12(16.6.29)738Chapter 16. Integration of Ordinary Differential ... calculatesdydx.{void lubksb(float **a, int n, int *indx, float b[]);void ludcmp(float **a, int n, int *indx, float *d);int i,j,nn,*indx;float d,h,x,**a,*del,*ytemp;indx=ivector(1,n);a=matrix(1,n,1,n);del=vector(1,n);ytemp=vector(1,n);h=htot/nstep; ... methods have been, we think, squeezed740Chapter 16. Integration of Ordinary Differential Equations Sample page from NUMERICAL RECIPES IN C: THE ART OF SCIENTIFIC COMPUTING (ISBN 0-521-43108-5)Copyright...
... methods have been, we think, squeezed752Chapter 16. Integration of Ordinary Differential Equations Sample page from NUMERICAL RECIPES IN C: THE ART OF SCIENTIFIC COMPUTING (ISBN 0-521-43108-5)Copyright ... methods in all applications. We are willing, however, to be corrected.CITED REFERENCES AND FURTHER READING:Gear, C.W. 1971,Numerical Initial Value Problems in Ordinary Differential Equations (EnglewoodCliffs, ... part of the procedure, and it is desirable to minimize its effect. Therefore, theintegration steps of a predictor-corrector method are overlapping, each one involvingseveral stepsize intervals...
... solving a largerproblem once only, where ease of programming outweighs expense of computertime. Occasionally, the sparse matrix methods of §2.7 are useful for solving a set of difference equations ... N grid points in O(N) operations.The “rapid” direct elliptic solvers discussed in §19.4 solve special kinds of elliptic equations in O(N log N) operations. The numerical coefficients in these ... the order of theinterpolation P (i.e., it interpolates polynomials of degree mp− 1 exactly). Supposemris the order of R,andthatRis the adjoint of some P (not necessarily the P youintend to...