gfuds_c |

## Procedurevoid gfuds_c ( void ( * udfuns ) ( SpiceDouble et, SpiceDouble * value ), void ( * udqdec ) ( void ( * udfuns ) ( SpiceDouble et, SpiceDouble * value ), SpiceDouble et, SpiceBoolean * isdecr ), ConstSpiceChar * relate, SpiceDouble refval, SpiceDouble adjust, SpiceDouble step, SpiceInt nintvls, SpiceCell * cnfine, SpiceCell * result ) ## AbstractPerform a GF search on a user defined scalar quantity. ## Required_ReadingGF WINDOWS ## KeywordsEVENT GEOMETRY SEARCH WINDOW ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- udfuns I Name of the routine that computes the scalar quantity of interest at some time. udqdec I Name of the routine that computes whether the scalar quantity is decreasing. relate I Operator that either looks for an extreme value (max, min, local, absolute) or compares the geometric quantity value and a number. refval I Value used as reference for scalar quantity condition. adjust I Allowed variation for absolute extremal geometric conditions. step I Step size used for locating extrema and roots. nintvls I Workspace window interval count cnfine I-O SPICE window to which the search is restricted. result O SPICE window containing results. ## Detailed_Inputudfuns the name of the external routine that returns the value of the scalar quantity of interest at time `et'. The calling sequence for "udfuns" is: udfuns ( et, &value ) where: et an input double precision value representing the TDB ephemeris seconds time at which to determine the scalar value. value is the value of the geometric quantity at `et'. udqdec the name of the external routine that determines if the scalar quantity calculated by "udfuns" is decreasing. The calling sequence for "udqdec" is: udqdec ( udfuns, et, &isdecr ) where: udfuns the name of the scalar function as defined above. et an input double precision value representing the TDB ephemeris seconds time at at which to determine the time derivative of `udfuns'. isdecr a logical variable indicating whether or not the scalar value returned by udfuns is decreasing. `isdecr' returns true if the time derivative of "udfuns" at `et' is negative. relate the scalar string comparison operator indicating the numeric constraint of interest. Values are: ">" value of scalar quantity greater than some reference (refval). "=" value of scalar quantity equal to some reference (refval). "<" value of scalar quantity less than some reference (refval). "ABSMAX" The scalar quantity is at an absolute maximum. "ABSMIN" The scalar quantity is at an absolute minimum. "LOCMAX" The scalar quantity is at a local maximum. "LOCMIN" The scalar quantity is at a local minimum. The caller may indicate that the region of interest is the set of time intervals where the quantity is within a specified distance of an absolute extremum. The argument `adjust' (described below) is used to specified this distance. Local extrema are considered to exist only in the interiors of the intervals comprising the confinement window: a local extremum cannot exist at a boundary point of the confinement window. `relate' is insensitive to case, leading and trailing blanks. refval is the reference value used to define an equality or inequality to satisfied by the scalar quantity. The units of refval are those of the scalar quantity. adjust the amount by which the quantity is allowed to vary from an absolute extremum. If the search is for an absolute minimum is performed, the resulting window contains time intervals when the geometric quantity value has values between ABSMIN and ABSMIN + adjust. If the search is for an absolute maximum, the corresponding range is between ABSMAX - adjust and ABSMAX. `adjust' is not used for searches for local extrema, equality or inequality conditions and must have value zero for such searches. step the double precision time step size to use in the search. `step' must be short enough to for a search using this step size to locate the time intervals where the scalar quantity function is monotone increasing or decreasing. However, `step' must not be *too* short, or the search will take an The choice of `step' affects the completeness but not the precision of solutions found by this routine; the precision is controlled by the convergence tolerance. See the discussion of the parameter SPICE_GF_CNVTOL for details. `step' has units of TDB seconds. nintvls an integer value specifying the number of intervals in the the internal workspace array used by this routine. `nintvls' should be at least as large as the number of intervals within the search region on which the specified observer-target vector coordinate function is monotone increasing or decreasing. It does no harm to pick a value of `nintvls' larger than the minimum required to execute the specified search, but if chosen too small, the search will fail. cnfine a double precision SPICE window that confines the time period over which the specified search is conducted. cnfine may consist of a single interval or a collection of intervals. In some cases the confinement window can be used to greatly reduce the time period that must be searched for the desired solution. See the Particulars section below for further discussion. See the Examples section below for a code example that shows how to create a confinement window. ## Detailed_Outputcnfine is the input confinement window, updated if necessary so the control area of its data array indicates the window's size and cardinality. The window data are unchanged. result is a SPICE window representing the set of time intervals, within the confinement period, when the specified geometric event occurs. If `result' is non-empty on input, its contents will be discarded before ## ParametersNone. ## Exceptions1) In order for this routine to produce correct results, the step size must be appropriate for the problem at hand. Step sizes that are too large may cause this routine to miss roots; step sizes that are too small may cause this routine to run unacceptably slowly and in some cases, find spurious roots. This routine does not diagnose invalid step sizes, except that if the step size is non-positive, an error is signaled by a routine in the call tree of this routine. 2) Due to numerical errors, in particular, - Truncation error in time values - Finite tolerance value - Errors in computed geometric quantities it is *normal* for the condition of interest to not always be satisfied near the endpoints of the intervals comprising the result window. The result window may need to be contracted slightly by the caller to achieve desired results. The SPICE window routine wncond_c can be used to contract the result window. 3) If an error (typically cell overflow) occurs while performing window arithmetic, the error will be diagnosed by a routine in the call tree of this routine. 4) If the relational operator `relate' is not recognized, an error is signaled by a routine in the call tree of this routine. 5) If `adjust' is negative, the error SPICE(VALUEOUTOFRANGE) will signal from a routine in the call tree of this routine. A non-zero value for `adjust' when `relate' has any value other than "ABSMIN" or "ABSMAX" causes the error SPICE(INVALIDVALUE) to signal from a routine in the call tree of this routine. 6) If required ephemerides or other kernel data are not available, an error is signaled by a routine in the call tree of this routine. 7) If the workspace interval count is less than 1, the error SPICE(VALUEOUTOFRANGE) will be signaled. 8) If the required amount of workspace memory cannot be allocated, the error SPICE(MALLOCFAILURE) will be signaled. 9) If any input string argument pointer is null, the error SPICE(NULLPOINTER) will be signaled. 10) If any input string argument is empty, the error SPICE(EMPTYSTRING) will be signaled. 11) If either input cell has type other than SpiceDouble, the error SPICE(TYPEMISMATCH) is signaled. ## FilesAppropriate kernels must be loaded by the calling program before this routine is called. If the user defined function requires access to ephemeris data: - SPK data: ephemeris data for any body over the time period defined by the confinement window must be loaded. If aberration corrections are used, the states of target and observer relative to the solar system barycenter must be calculable from the available ephemeris data. Typically ephemeris data are made available by loading one or more SPK files via furnsh_c. - If non-inertial reference frames are used, then PCK files, frame kernels, C-kernels, and SCLK kernels may be needed. In all cases, kernel data are normally loaded once per program run, NOT every time this routine is called. ## ParticularsThis routine determines a set of one or more time intervals within the confinement window when the scalar function satisfies a caller-specified constraint. The resulting set of intervals is returned as a SPICE window. Below we discuss in greater detail aspects of this routine's solution process that are relevant to correct and efficient use of this routine in user applications. udqdec Default Template ======================= The user must supply a routine to determine whether sign of the time derivative of udfuns is positive or negative at `et'. For cases where udfuns is numerically well behaved, the user may find it convenient to use a routine based on the below template. uddc_c determines the truth of the expression d (udfuns) -- < 0 dt using the library routine uddf_c to numerically calculate the derivative of udfuns using a three-point estimation. Use of gfdecr requires only changing the "udfuns" argument to that of the user provided scalar function passed to ## ExamplesThe numerical results shown for these examples may differ across platforms. The results depend on the SPICE kernels used as input, the compiler and supporting libraries, and the machine specific arithmetic implementation. Conduct a search on the range rate of the vector from the Sun to the Moon. Define a function to calculate the value. Use the meta-kernel shown below to load the required SPICE kernels. KPL/MK File name: standard.tm This meta-kernel is intended to support operation of SPICE example programs. The kernels shown here should not be assumed to contain adequate or correct versions of data required by SPICE-based user applications. In order for an application to use this meta-kernel, the kernels referenced here must be present in the user's current working directory. \begindata KERNELS_TO_LOAD = ( 'de414.bsp', 'pck00008.tpc', 'naif0009.tls' ) \begintext Code: #include <stdio.h> #include <stdlib.h> #include <string.h> #include "SpiceUsr.h" #include "SpiceZfc.h" #define MAXWIN 20000 #define TIMFMT "YYYY-MON-DD HR:MN:SC.###" #define TIMLEN 41 #define NLOOPS 7 void gfq ( SpiceDouble et, SpiceDouble * value ); void gfdecrx ( void ( * udfuns ) ( SpiceDouble et, SpiceDouble * value ), SpiceDouble et, SpiceBoolean * isdecr ); doublereal dvnorm_(doublereal *state); int main( int argc, char **argv ) { /. Create the needed windows. Note, one interval consists of two values, so the total number of cell values to allocate is twice the number of intervals. ./ SPICEDOUBLE_CELL ( result, 2*MAXWIN ); SPICEDOUBLE_CELL ( cnfine, 2 ); SpiceDouble begtim; SpiceDouble endtim; SpiceDouble step; SpiceDouble adjust; SpiceDouble refval; SpiceDouble beg; SpiceDouble end; SpiceChar begstr [ TIMLEN ]; SpiceChar endstr [ TIMLEN ]; SpiceInt count; SpiceInt i; SpiceInt j; ConstSpiceChar * relate [NLOOPS] = { "=", "<", ">", "LOCMIN", "ABSMIN", "LOCMAX", "ABSMAX" }; printf( "Compile date %s, %s\n\n", __DATE__, __TIME__ ); /. Load kernels. ./ furnsh_c( "standard.tm" ); /. Store the time bounds of our search interval in the `cnfine' confinement window. ./ str2et_c( "2007 JAN 01", &begtim ); str2et_c( "2007 APR 01", &endtim ); wninsd_c ( begtim, endtim, &cnfine ); /. Search using a step size of 1 day (in units of seconds). The reference value is .3365 km/s. We're not using the adjustment feature, so we set `adjust' to zero. ./ step = spd_c(); adjust = 0.; refval = .3365; for ( j = 0; j < NLOOPS; j++ ) { printf ( "Relation condition: %s \n", relate[j] ); /. Perform the search. The SPICE window `result' contains the set of times when the condition is met. ./ ## Restrictions1) Any kernel files required by this routine must be loaded before this routine is called. ## Literature_ReferencesNone. ## Author_and_InstitutionN.J. Bachman (JPL) E.D. Wright (JPL) ## Version-CSPICE Version 1.1.0, 21-OCT-2013 (NJB)(EDW) Correction to description of UDQDEC to show UDFUNC as an argument. Header was updated to discuss use of gfstol_c. Edit to comments to correct search description; eliminate typo in gfq Abstract, "range rate" instead of "range." Improved header detail describing convergence tolerance. -CSPICE Version 1.0.0, 22-FEB-2010 (EDW) ## Index_EntriesGF user defined scalar function search |

Wed Apr 5 17:54:36 2017