European Space Agency

Royal Belgian Institute for Aeronomy

uf426 - interpolating an extremum of B

subroutine  uf426(bextr, aextr, ktype, ifail)

Parameters:

• bextr [real8,out] :: Magnetic field intensity at the extremum

• aextr [real8,out] :: Altitude at the extremum

• ktype [integer4,out] :: Type of extremum (-1; +1)

• ifail [integer4,out] :: error flag (see Diagnostics)

Description

The subroutine uf426() interpolates an extremum of the magnetic field intensity along a magnetic field line. To be used, the common block uc170 has to include at least three points and the last Runge-Kutta step had to overreach the extremum. The subroutine uf426() combines parabolic interpolations and Runge-Kutta steps to determine the correct location of the extremum. Note that the two last points stored in the common block uc170 can be modified and that a new point can be added by the subroutine.

When the subroutine succeeds, the arguments bextr and aextr are set to the magnetic field intensity and altitude at the extremum location, respectively. The argument ktype is set to 1 when the extremum is a maximum and to -1 for a minimum. The index in the common block uc170 corresponding to the extremum is stored in the argument ifail.

Note

The subroutine takes into account the step size limit stplst defined in the common block uc190.

Diagnostics

• -42601, two points are identical

• -42602, B does not vary

• -42603, too many iterations

• -42604, -42605, problem with the Runge Kutta step

• -42606, too many iterations

Common Blocks

• uc160 - general constants

• uc170 - temporary magnetic field line

• uc190 - control parameters, set 1

Dependencies

Called by

• uf422 - follow a field line until a boundary condition is reached

Calls

• uf423 - Runge Kutta step

See also

None

Reported Bugs

• 18-Dec-97(v1.11), Malfunction of subroutine uf426()

Examples

None

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UNILIB/tags/v3.02