# naginterfaces.library.pde.dim1_​parab_​remesh_​keller¶

naginterfaces.library.pde.dim1_parab_remesh_keller(npde, ts, tout, pdedef, bndary, uvinit, u, x, nleft, nv, xi, rtol, atol, itol, norm, laopt, algopt, remesh, xfix, nrmesh, dxmesh, trmesh, ipminf, comm, itask, itrace, ind, odedef=None, xratio=1.5, con=None, monitf=None, lrsave_estim=0, lisave_estim=0, data=None, io_manager=None, spiked_sorder='C')[source]

dim1_parab_remesh_keller integrates a system of linear or nonlinear, first-order, time-dependent partial differential equations (PDEs) in one space variable, with scope for coupled ordinary differential equations (ODEs), and automatic adaptive spatial remeshing. The spatial discretization is performed using the Keller box scheme (see Keller (1970)) and the method of lines is employed to reduce the PDEs to a system of ODEs. The resulting system is solved using a Backward Differentiation Formula (BDF) method or a Theta method (switching between Newton’s method and functional iteration).

For full information please refer to the NAG Library document for d03pr

https://www.nag.com/numeric/nl/nagdoc_27.3/flhtml/d03/d03prf.html

Parameters
npdeint

The number of PDEs to be solved.

tsfloat

The initial value of the independent variable .

toutfloat

The final value of to which the integration is to be carried out.

pdedefcallable (res, ires) = pdedef(t, x, u, ut, ux, v, vdot, ires, data=None)

must evaluate the functions which define the system of PDEs. is called approximately midway between each pair of mesh points in turn by dim1_parab_remesh_keller.

Parameters
tfloat

The current value of the independent variable .

xfloat

The current value of the space variable .

ufloat, ndarray, shape

contains the value of the component , for .

utfloat, ndarray, shape

contains the value of the component , for .

uxfloat, ndarray, shape

contains the value of the component , for .

vfloat, ndarray, shape

If , contains the value of the component , for .

vdotfloat, ndarray, shape

If , contains the value of component , for .

iresint

The form of that must be returned in the array .

Equation (9) must be used.

Equation (0) must be used.

dataarbitrary, optional, modifiable in place

User-communication data for callback functions.

Returns
resfloat, array-like, shape

must contain the th component of , for , where is defined as

i.e., only terms depending explicitly on time derivatives, or

i.e., all terms in equation (3).

The definition of is determined by the input value of .

iresint

Should usually remain unchanged. However, you may set to force the integration function to take certain actions, as described below:

Indicates to the integrator that control should be passed back immediately to the calling function with the error indicator set to = 6.

Indicates to the integrator that the current time step should be abandoned and a smaller time step used instead. You may wish to set when a physically meaningless input or output value has been generated. If you consecutively set , dim1_parab_remesh_keller returns to the calling function with the error indicator set to = 4.

bndarycallable (res, ires) = bndary(t, ibnd, nobc, u, ut, v, vdot, ires, data=None)

must evaluate the functions and which describe the boundary conditions, as given in (5) and (6).

Parameters
tfloat

The current value of the independent variable .

ibndint

Specifies which boundary conditions are to be evaluated.

must compute the left-hand boundary condition at .

must compute of the right-hand boundary condition at .

nobcint

Specifies the number of boundary conditions at the boundary specified by .

ufloat, ndarray, shape

contains the value of the component at the boundary specified by , for .

utfloat, ndarray, shape

contains the value of the component , for .

vfloat, ndarray, shape

If , contains the value of the component , for .

vdotfloat, ndarray, shape

If , contains the value of component , for .

Note: , for , may only appear linearly as in (1) and (2).

iresint

The form of (or ) that must be returned in the array .

Equation (1) must be used.

Equation (2) must be used.

dataarbitrary, optional, modifiable in place

User-communication data for callback functions.

Returns
resfloat, array-like, shape

must contain the th component of or , depending on the value of , for , where is defined as

i.e., only terms depending explicitly on time derivatives, or

i.e., all terms in equation (7), and similarly for .

The definitions of and are determined by the input value of .

iresint

Should usually remain unchanged. However, you may set to force the integration function to take certain actions as described below:

Indicates to the integrator that control should be passed back immediately to the calling function with the error indicator set to = 6.

Indicates to the integrator that the current time step should be abandoned and a smaller time step used instead. You may wish to set when a physically meaningless input or output value has been generated. If you consecutively set , dim1_parab_remesh_keller returns to the calling function with the error indicator set to = 4.

uvinitcallable (u, v) = uvinit(npde, x, xi, nv, data=None)

must supply the initial values of and for all values of in the interval .

Parameters
npdeint

The number of PDEs in the system.

xfloat, ndarray, shape

The current mesh. contains the value of , for .

xifloat, ndarray, shape

If , contains the ODE/PDE coupling point, , for .

nvint

The number of coupled ODEs in the system.

dataarbitrary, optional, modifiable in place

User-communication data for callback functions.

Returns
ufloat, array-like, shape

contains the value of the component , for , for .

vfloat, array-like, shape

If , must contain the value of component , for .

ufloat, array-like, shape

If the value of must be unchanged from the previous call.

xfloat, array-like, shape

The initial mesh points in the space direction. must specify the left-hand boundary, , and must specify the right-hand boundary, .

nleftint

The number of boundary conditions at the left-hand mesh point .

nvint

The number of coupled ODE components.

xifloat, array-like, shape

, for , must be set to the ODE/PDE coupling points, .

rtolfloat, array-like, shape

Note: the required length for this argument is determined as follows: if : ; if : ; otherwise: .

The relative local error tolerance.

atolfloat, array-like, shape

Note: the required length for this argument is determined as follows: if : ; if : ; otherwise: .

The absolute local error tolerance.

itolint

A value to indicate the form of the local error test. indicates to dim1_parab_remesh_keller whether to interpret either or both of or as a vector or scalar.

normstr, length 1

The type of norm to be used.

Maximum norm.

Averaged norm.

If denotes the norm of the vector of length , then for the averaged norm

while for the maximum norm

See the description of for the formulation of the weight vector .

laoptstr, length 1

The type of matrix algebra required.

Full matrix methods to be used.

Banded matrix methods to be used.

Sparse matrix methods to be used.

algoptfloat, array-like, shape

May be set to control various options available in the integrator. If you wish to employ all the default options, should be set to . Default values will also be used for any other elements of set to zero. The permissible values, default values, and meanings are as follows:

Selects the ODE integration method to be used. If , a BDF method is used and if , a Theta method is used. The default value is .

If , then , for , are not used.

Specifies the maximum order of the BDF integration formula to be used. may be , , , or . The default value is .

Specifies what method is to be used to solve the system of nonlinear equations arising on each step of the BDF method. If a modified Newton iteration is used and if a functional iteration method is used. If functional iteration is selected and the integrator encounters difficulty, there is an automatic switch to the modified Newton iteration. The default value is .

Specifies whether or not the Petzold error test is to be employed. The Petzold error test results in extra overhead but is more suitable when algebraic equations are present, such as , for , for some or when there is no dependence in the coupled ODE system. If , the Petzold test is used. If , the Petzold test is not used. The default value is .

If , , for , are not used.

Specifies the value of Theta to be used in the Theta integration method. . The default value is .

Specifies what method is to be used to solve the system of nonlinear equations arising on each step of the Theta method. If , a modified Newton iteration is used and if , a functional iteration method is used. The default value is .

Specifies whether or not the integrator is allowed to switch automatically between modified Newton and functional iteration methods in order to be more efficient. If , switching is allowed and if , switching is not allowed. The default value is .

Specifies a point in the time direction, , beyond which integration must not be attempted. The use of is described under the argument . If , a value of , for , say, should be specified even if subsequently specifies that will not be used.

Specifies the minimum absolute step size to be allowed in the time integration. If this option is not required, should be set to .

Specifies the maximum absolute step size to be allowed in the time integration. If this option is not required, should be set to .

Specifies the initial step size to be attempted by the integrator. If , the initial step size is calculated internally.

Specifies the maximum number of steps to be attempted by the integrator in any one call. If , no limit is imposed.

Specifies what method is to be used to solve the nonlinear equations at the initial point to initialize the values of , , and . If , a modified Newton iteration is used and if , functional iteration is used. The default value is .

and are used only for the sparse matrix algebra option, i.e., .

Governs the choice of pivots during the decomposition of the first Jacobian matrix. It should lie in the range , with smaller values biasing the algorithm towards maintaining sparsity at the expense of numerical stability. If lies outside this range then the default value is used. If the functions regard the Jacobian matrix as numerically singular then increasing towards may help, but at the cost of increased fill-in. The default value is .

Used as a relative pivot threshold during subsequent Jacobian decompositions (see ) below which an internal error is invoked. must be greater than zero, otherwise the default value is used. If is greater than no check is made on the pivot size, and this may be a necessary option if the Jacobian is found to be numerically singular (see ). The default value is .

remeshbool

Indicates whether or not spatial remeshing should be performed.

Indicates that spatial remeshing should be performed as specified.

Indicates that spatial remeshing should be suppressed.

Note: should not be changed between consecutive calls to dim1_parab_remesh_keller. Remeshing can be switched off or on at specified times by using appropriate values for the arguments and at each call.

xfixfloat, array-like, shape

, for , must contain the value of the coordinate at the th fixed mesh point.

nrmeshint

Indicates the form of meshing to be performed.

Indicates that a new mesh is adopted according to the argument . The mesh is tested every timesteps.

Indicates that remeshing should take place just once at the end of the first time step reached when .

Indicates that remeshing will take place every time steps, with no testing using .

Note: may be changed between consecutive calls to dim1_parab_remesh_keller to give greater flexibility over the times of remeshing.

dxmeshfloat

Determines whether a new mesh is adopted when is set less than zero. A possible new mesh is calculated at the end of every time steps, but is adopted only if

or

thus imposes a lower limit on the difference between one mesh and the next.

trmeshfloat

Specifies when remeshing will take place when is set to zero. Remeshing will occur just once at the end of the first time step reached when is greater than .

Note: may be changed between consecutive calls to dim1_parab_remesh_keller to force remeshing at several specified times.

ipminfint

The level of trace information regarding the adaptive remeshing. Details are directed to the file object associated with the advisory I/O unit (see FileObjManager).

No trace information.

Brief summary of mesh characteristics.

More detailed information, including old and new mesh points, mesh sizes and monitor function values.

commdict, communication object, modified in place

Note: this argument will be (re-)initialized when it is an empty dict or under the following condition: .

Communication structure.

On initial entry: need not be set.

itaskint

The task to be performed by the ODE integrator.

Normal computation of output values at (by overshooting and interpolating).

Take one step in the time direction and return.

Stop at first internal integration point at or beyond .

Normal computation of output values at but without overshooting where is described under the argument .

Take one step in the time direction and return, without passing , where is described under the argument .

itraceint

The level of trace information required from dim1_parab_remesh_keller and the underlying ODE solver as follows:

No output is generated.

Only warning messages from the PDE solver are printed.

Output from the underlying ODE solver is printed. This output contains details of Jacobian entries, the nonlinear iteration and the time integration during the computation of the ODE system.

Output from the underlying ODE solver is similar to that produced when , except that the advisory messages are given in greater detail.

The output from the underlying ODE solver is similar to that produced when , except that the advisory messages are given in greater detail.

You are advised to set , unless you are experienced with submodule ode.

indint

Indicates whether this is a continuation call or a new integration.

Starts or restarts the integration in time.

Continues the integration after an earlier exit from the function. In this case, only the argument and the remeshing arguments , , , and may be reset between calls to dim1_parab_remesh_keller.

odedefNone or callable (r, ires) = odedef(t, v, vdot, xi, ucp, ucpx, ucpt, ires, data=None), optional

Note: if this argument is None then a NAG-supplied facility will be used.

must evaluate the functions , which define the system of ODEs, as given in (4).

If you wish to compute the solution of a system of PDEs only (i.e., ), must be None.

Parameters
tfloat

The current value of the independent variable .

vfloat, ndarray, shape

If , contains the value of the component , for .

vdotfloat, ndarray, shape

If , contains the value of component , for .

xifloat, ndarray, shape

If , contains the ODE/PDE coupling point, , for .

ucpfloat, ndarray, shape

If , contains the value of at the coupling point , for , for .

ucpxfloat, ndarray, shape

If , contains the value of at the coupling point , for , for .

ucptfloat, ndarray, shape

If , contains the value of at the coupling point , for , for .

iresint

The form of that must be returned in the array .

Equation (3) must be used.

Equation (4) must be used.

dataarbitrary, optional, modifiable in place

User-communication data for callback functions.

Returns
rfloat, array-like, shape

If , must contain the th component of , for , where is defined as

i.e., only terms depending explicitly on time derivatives, or

i.e., all terms in equation (4). The definition of is determined by the input value of .

iresint

Should usually remain unchanged. However, you may reset to force the integration function to take certain actions, as described below:

Indicates to the integrator that control should be passed back immediately to the calling function with the error indicator set to = 6.

Indicates to the integrator that the current time step should be abandoned and a smaller time step used instead. You may wish to set when a physically meaningless input or output value has been generated. If you consecutively set , dim1_parab_remesh_keller returns to the calling function with the error indicator set to = 4.

xratiofloat, optional

An input bound on the adjacent mesh ratio (greater than and typically in the range to ). The remeshing functions will attempt to ensure that

conNone or float, optional

Note: if this argument is None then a default value will be used, determined as follows: .

An input bound on the sub-integral of the monitor function over each space step. The remeshing functions will attempt to ensure that

(see Furzeland (1984)). gives you more control over the mesh distribution e.g., decreasing allows more clustering. A typical value is , but you are encouraged to experiment with different values. Its value is not critical and the mesh should be qualitatively correct for all values in the range given below.

monitfNone or callable fmon = monitf(t, x, u, data=None), optional

Note: if this argument is None then a NAG-supplied facility will be used.

must supply and evaluate a remesh monitor function to indicate the solution behaviour of interest.

If you specify , i.e., no remeshing, will not be called and may be None.

Parameters
tfloat

The current value of the independent variable .

xfloat, ndarray, shape

The current mesh. contains the value of , for .

ufloat, ndarray, shape

contains the value of at and time , for , for .

dataarbitrary, optional, modifiable in place

User-communication data for callback functions.

Returns
fmonfloat, array-like, shape

must contain the value of the monitor function at mesh point .

lrsave_estimint, optional

When performing a new integration, the size to use for the communication array [‘rsave’].

Otherwise, the value has no effect.

An initial estimate for an adequate is computed by the function.

If your supplied is too small, the estimated value will be used instead.

In some cases the estimated value will be sufficient for continuation calls to the function.

When , even the function’s initial estimated value of may be too small.

If so, the function returns with = 15.

You are advised to call the function again with and set to at least the lower-bound value returned in , then make the desired subsequent calls with , then repeat the process if necessary.

lisave_estimint, optional

When performing a new integration, the size to use for the communication array [‘isave’].

Otherwise, the value has no effect.

An initial estimate for an adequate is computed by the function.

If your supplied is too small, the estimated value will be used instead.

In some cases the estimated value will be sufficient for continuation calls to the function.

When , even the function’s initial estimated value of may be too small.

If so, the function returns with = 15.

You are advised to call the function again with and set to at least the lower-bound value returned in , then make the desired subsequent calls with , then repeat the process if necessary.

dataarbitrary, optional

User-communication data for callback functions.

io_managerFileObjManager, optional

Manager for I/O in this routine.

spiked_sorderstr, optional

If in is spiked (i.e., has unit extent in all but one dimension, or has size ), selects the storage order to associate with it in the NAG Engine:

spiked_sorder =

row-major storage will be used;

spiked_sorder =

column-major storage will be used.

Returns
tsfloat

The value of corresponding to the solution values in . Normally .

ufloat, ndarray, shape

The computed solution , for , for , and , for , evaluated at , as follows:

contain , for , for , and

contain , for .

xfloat, ndarray, shape

The final values of the mesh points.

indint

.

lrsave_minint

A lower bound on the sufficient size for [‘rsave’].

lisave_minint

A lower bound on the sufficient size for [‘isave’].

Raises
NagValueError
(errno )

On entry, on initial entry .

Constraint: on initial entry .

(errno )

On entry, the point does not coincide with any : and .

(errno )

On entry, , and .

Constraint: .

(errno )

On entry, at least one point in lies outside : and .

(errno )

On entry, , and .

Constraint: .

(errno )

On entry, and .

Constraint: corresponding elements and cannot both be .

(errno )

On entry, and .

Constraint: .

(errno )

On entry, and .

Constraint: .

(errno )

On entry, .

Constraint: , , or .

(errno )

On entry, , , and .

Constraint: .

(errno )

On entry, , , and .

Constraint: .

(errno )

On entry, , .

Constraint: .

(errno )

On entry, , .

Constraint: .

(errno )

On entry, .

Constraint: .

(errno )

On entry, .

Constraint: , or .

(errno )

On entry, .

Constraint: .

(errno )

On entry, , .

Constraint: .

(errno )

On entry, .

Constraint: .

(errno )

On entry, and .

Constraint: when .

(errno )

On entry, and .

Constraint: when .

(errno )

On entry, , .

Constraint: .

(errno )

On entry, .

Constraint: .

(errno )

On entry, .

Constraint: .

(errno )

On entry, .

Constraint: .

(errno )

On entry, .

Constraint: , or .

(errno )

On entry, .

Constraint: or .

(errno )

On entry, .

Constraint: or .

(errno )

On entry, .

Constraint: , , , or .

(errno )

On entry, .

Constraint: .

(errno )

On entry, is too small: and .

(errno )

On entry, and .

Constraint: .

(errno )

In setting up the ODE system an internal auxiliary was unable to initialize the derivative. This could be due to your setting in or .

(errno )

Singular Jacobian of ODE system. Check problem formulation.

(errno )

and were too small to start integration.

(errno )

set to an invalid value in call to , , or .

(errno )

Serious error in internal call to an auxiliary. Increase for further details.

(errno )

Error during Jacobian formulation for ODE system. Increase for further details.

(errno )

In solving ODE system, the maximum number of steps has been exceeded. .

(errno )

has been changed between calls to dim1_parab_remesh_keller.

Warns
NagAlgorithmicWarning
(errno )

Underlying ODE solver cannot make further progress from the point with the supplied values of and . .

(errno )

Repeated errors in an attempted step of underlying ODE solver. Integration was successful as far as : .

(errno )

In evaluating residual of ODE system, has been set in , , or . Integration is successful as far as : .

(errno )

Integration completed, but small changes in or are unlikely to result in a changed solution.

(errno )

Zero error weights encountered during time integration.

(errno )

When using the sparse option, or is too small: , .

Notes

dim1_parab_remesh_keller integrates the system of first-order PDEs and coupled ODEs given by the master equations:

In the PDE part of the problem given by (1), the functions must have the general form

where , and depend on , , , and .

The vector is the set of PDE solution values

and the vector is the partial derivative with respect to . The vector is the set of ODE solution values

and denotes its derivative with respect to time.

In the ODE part given by (2), represents a vector of spatial coupling points at which the ODEs are coupled to the PDEs. These points may or may not be equal to some of the PDE spatial mesh points. , and are the functions , and evaluated at these coupling points. Each may only depend linearly on time derivatives. Hence equation (2) may be written more precisely as

where , is a vector of length , is an by matrix, is an by matrix and the entries in , and may depend on , , , and . In practice you only need to supply a vector of information to define the ODEs and not the matrices and . (See Parameters for the specification of .)

The integration in time is from to , over the space interval , where and are the leftmost and rightmost points of a mesh defined initially by you and (possibly) adapted automatically during the integration according to user-specified criteria.

The PDE system which is defined by the functions must be specified in .

The initial values of the functions and must be specified in . Note that will be called again following any remeshing, and so should be specified for all values of in the interval , and not just the initial mesh points.

For a first-order system of PDEs, only one boundary condition is required for each PDE component . The boundary conditions are separated into at the left-hand boundary , and at the right-hand boundary , such that . The position of the boundary condition for each component should be chosen with care; the general rule is that if the characteristic direction of at the left-hand boundary (say) points into the interior of the solution domain, then the boundary condition for should be specified at the left-hand boundary. Incorrect positioning of boundary conditions generally results in initialization or integration difficulties in the underlying time integration functions.

The boundary conditions have the master equation form:

at the left-hand boundary, and

at the right-hand boundary.

Note that the functions and must not depend on , since spatial derivatives are not determined explicitly in the Keller box scheme functions. If the problem involves derivative (Neumann) boundary conditions then it is generally possible to restate such boundary conditions in terms of permissible variables. Also note that and must be linear with respect to time derivatives, so that the boundary conditions have the general form:

at the left-hand boundary, and