Adams Basic Package > Adams Solver > Welcome to Adams Solver Subroutines > User-Written Subroutines > VTOSUB

VTOSUB

The VTOSUB evaluation subroutine computes torque components for a VTORQUE statement (C++ or FORTRAN). VTOSUB is optional. You only need it if you don't want to use function expressions in the VTORQUE statement.
 
Note:  
Use mixed case names for the Adams subroutine names when using the C style interface. For the default subroutine name capitalize the first letter and have the remaining letters lower case; Vtosub for example. Doing this ensures that Adams Solver correctly distinguishes a C style subroutine from Fortran and calls with the appropriate interface.

Use

Corresponding Statement

Calling Sequence

SUBROUTINE VTOSUB(id, time, par, npar, dflag, iflag, result)

Input Arguments

 
id
An integer variable that contains the ID of the VTORQUE statement requesting information from VTOSUB. From the identifier, Adams Solver automatically recognizes other information (such as the par argument) that is available in the corresponding statement.
time
A double-precision variable through which Adams Solver conveys the current simulation time.
par
A double-precision array of constants taken in order from the USER parenthetical list of the VTORQUE statement.
npar
An integer variable that indicates the number of constants you specify in the USER parenthetical list. The primary purpose of the npar argument is to provide VTOSUB with the number of values stored in the par array.
dflag
A logical variable that Adams Solver sets to true when it calls VTOSUB to evaluate the partial derivatives of the specified functions. Otherwise, Adams Solver sets the dflag argument to false.
iflag
An integer variable that Adams Solver sets to indicate why the routine is being called:
Adams Solver sets iflag to 3 when it needs the functional dependency of the user-defined variable. The functional dependencies are set with the same calls to the SYSARY and SYSFNC utility subroutines that are made to compute the value of the user-defined variable. If iflag is 0, Adams Solver computes the value of the user-written variable.
When your user-defined subroutine has static data that needs to be saved and restored to support the Adams Solver commands Save and Reload, then call the serialization functions for your data when iflag is set to 7, and the un-serialization functions when iflag is set to 9.
Note: In simple subroutines where serializing data is not needed, you can declare iflag as a logical variable. In this case you declare your dependencies when Adams Solver sets iflag to true, and compute the subroutine's value when Adams Solver sets iflag to false.

Output Arguments

 
result
A double-precision array of length 3 that returns the x-, y-, and z-components of the VTORQUE.

Extended Definition

You can often use the VTORQUE statement with function expressions sufficient to define the three rotational vector components of a torque at a point. However, if the torque expressions become lengthy and awkward, you can use a VTOSUB evaluation subroutine. If the algorithms use or consist of already existing FORTRAN-77 subroutines, VTOSUB can be made to call them.
You can call utility subroutines, such as AKISPL, CUBSPL, SYSARY and SYSFNC, from VTOSUB to obtain information about system variables, user-defined variables, and splines. See AKISPL, CUBSPL, SYSARY, and SYSFNC.
The SYSARY and SYSFNC utility subroutines automatically set functional dependencies when the VTOSUB argument iflag is not zero. In order for Adams Solver to compute solutions efficiently, it must know on which other variables each user-defined variable depends directly. Adams Solver determines these functional dependencies at the beginning of the simulation by calling VTOSUB with the argument iflag set to not zero. Adams Solver does this once for each VTORQUE statement with a FUNCTION=USER() argument.
During each call to the VTOSUB evaluation subroutine, Adams Solver records which calls you make to SYSARY and SYSFNC and assumes that the resulting values are dependent on only those Adams Solver variables accessed through the SYSARY and SYSFNC calls.
 
Tip:  
If the SYSARY or SYSFNC utility subroutines are called to access angular displacements, the values returned by these may contain discontinuities. To avoid the discontinuities, use the RCNVRT utility subroutine to convert the rotational angles from Euler angles to some other coordinate system that does not encounter a singularity.
 
Caution:  
■When the iflag argument is not zero, you must make all the same calls to SYSARY and SYSFNC as are made to compute the component values of VTORQUE. This ensures that Adams Solver has the proper functional dependencies. In general, failure to account for dependencies in the VTORQUE components may make it difficult for Adams Solver to converge to a solution and/or may force Adams Solver to take small integration steps, potentially causing large increases in execution time.
■When the iflag argument is not zero, SYSARY and SYSFNC return zero values for system and user-defined variables. When you execute Adams Solver, computations that divide by these values result in fatal errors. You should check for nonzero values or ensure the iflag argument is set to zero before dividing by these values.

FORTRAN - Prototype

A sample structure for VTOSUB is shown next. The comments explain how the subroutine works.
      SUBROUTINE VTOSUB(ID, TIME, PAR, NPAR, DFLAG,
     &                  IFLAG, RESULT)
C
C === Type and dimension statements ===================
C
C - External variable definitions -----------
C
      INTEGER                             ID
      DOUBLE PRECISION                    TIME
      DOUBLE PRECISION                    PAR(*)
      INTEGER                             NPAR
      LOGICAL                             DFLAG
      INTEGER                             IFLAG
      DOUBLE PRECISION                    RESULT(3)
C
C  ID           Identifier of calling VTORQUE statement
C  TIME         Current time
C  PAR          Array containing passed parameters
C  NPAR         Number of passed parameters
C  DFLAG        Differencing flag
C  IFLAG        Initial pass flag
C  RESULT       Array (dimension 3) of computed VTORQUE
C               components returned to ADAMS
C
C - Local variable and parameter definitions ------
C
      ...
C
C === Executable code =================================
C
C Assign readable variable names to passed parameters
C
      ...
C
C Call SYSFNC and/or SYSARY to collect information for
C the following calculations. Note: if IFLAG is true, these
C calls are actually setting functional dependencies.
C
      CALL SYSFNC (...)
C
C Check SYSFNC call through ERRMES utility routine
C
      CALL ERRMES (...)
C
C Repeat for all required SYSFNC or SYSARY calls
C
      ...
C
      IF (IFLAG) THEN
C
C - Subroutine initialization -------------
C
       ...
C
      ENDIF
C
C - Evaluate VTORQUE components ------------
C
C Your algorithms
C
      ...
C
C Assign values to the RESULT array
C
      RESULT(1) = ...
      RESULT(2) = ...
      RESULT(3) = ...
C
      RETURN
      END

C Style - Prototype

typedef void adams_c_VTOSUB(const struct sAdamsVtorque* vto, double TIME, int DFLAG, int IFLAG, double* RESULT);
/*
* VTORQUE -----------------------------------------------------------------
*/
struct sAdamsVtorque
{
int ID;
int NPAR;
const double* PAR;
int I;
int JFLOAT;
int RM;
};
 

Examples

For an example of this subroutine, see vtosub.f.