What is the Calling Sequence?

The C and Fortran77 interfaces, as they are not object-capable, need to use specific calling sequences that are more involved than the ones used from Matlab or Mathematica. In the Section called NetSolve Problem Specification in Chapter 4, we described the input and output arguments of a NetSolve problem as lists of objects. The Matlab and Mathematica interfaces to NetSolve can manipulate objects directly and it is therefore very easy to call NetSolve from their interfaces once problem descriptions are known. From interfaces that are not object-oriented (C and Fortran), it is necessary to use a calling sequence that describes the objects' features individually. For complete details, the user should refer to Chapter 5 and the Section called Sparse Matrix Representation in NetSolve in Chapter 17.

Let us take a very simple example: the user wants to perform a dense linear system solve. The first thing to know, as stated in earlier chapters, is the name or IP address of a host running a NetSolve agent. The default NetSolve agent running at the University of Tennessee is aware of many servers that can perform the computation. In fact, a dense linear system solve is provided with the NetSolve distribution as default numerical software for the server. The user has now two possible courses of action to find out about the problem. Let us assume that the user chooses to use the UNIX command line management tools (see Chapter 16 for a complete description of these tools). The alternative would be to use the CGI scripts on the NetSolve homepage.

the Section called Expanding the Server Capabilities in Chapter 13 shows how the servers specify the calling sequence to a given problem. It is usual for servers to enforce the same calling sequence as the original numerical software and to give a problem the name of the original library function. In the example, dgesv() is the name of an LAPACK subroutine and the user can therefore expect the calling sequence for the problem dgesv to match the one of the subroutine. One can see in the problem list returned by NS_problems a problem called linsol. In this example, linsol is a simplified version of dgesv and has a simplified calling sequence chosen by whomever started the first server that provides access to that problem. Since linsol is not the name of an LAPACK subroutine, its calling sequence can be arbitrary.
UNIX> NS_problems netsolve.cs.utk.edu

Next, two situations are possible. First, the user already knows the numerical software (e.g., LAPACK) and may even have code already written in terms of this software. In this case, the switching to NetSolve is immediate. The second possibility is that the user does not know the software. If this is the case, he needs to pay close attention to the output given by NS_probdesc. The output from this command first gives the calling sequence as it would be invoked from Matlab, and then gives the calling sequence from C/Fortran.
UNIX> NS_probdesc netsolve.cs.utk.edu dgesv
-- dgesv -- From LAPACK -
Compute the solution to a real system of linear equations
  A * X = b
where A is an N-by-B matrix and X and B are N-by-NRHS matrices.
Matlab Example : [x y z info ] = netsolve('dgesv',a,b)
* 2 objects in INPUT
 - input 0: Matrix Double Precision Real.
 Matrix A
 - input 1: Matrix Double Precision Real.
 Right hand side
* 4 objects in OUTPUT
 - output 0: Matrix Double Precision Real.
 LU factors ( A = P*L*U)
 - output 1: Vector Integer.
 Vector of pivots (defines the P matrix)
 - output 2: Matrix Double Precision Real.
 - output 3: Scalar Integer.
  0  successful
  <0 error on calling ?
  >0 QR algorithm failed
* Calling sequence from C or Fortran
8 arguments
 - Argument #0:
   - number of rows of input object #0 (A)
   - number of columns of input object #0 (A)
   - number of rows of input object #1 (RHS)
 - Argument #1:
   - number of columns of input object #1 (RHS)
 - Argument #2:
   - pointer to input object #0 (A)
   - pointer to output object #0 (LU)
   - pointer to output object #0 (LU)
 - Argument #3:
   - leading dimension of input object #0 (A)
 - Argument #4:
   - pointer to output object #1 (PIVOT)
 - Argument #5:
   - pointer to input object #1 (RHS)
   - pointer to output object #1 (PIVOT)
   - pointer to output object #2 (SOLUTION)
 - Argument #6:
   - leading dimension of input object #1 (RHS)
 - Argument #7:
   - pointer to output object #3 (INFO)

This output can appear rather cryptic at first. Let us work through it step by step. First, the number of arguments in the calling sequence is 8. This means that the call from C will look like:
status = netsl('dgesv()',X0,X1,X2,X3,X4,X5,X6,X7);
And from Fortran77, the call to NetSolve would be:
CALL FNETSL('dgesv()',STATUS,X0,X1,X2,X3,X4,X5,X6,X7)
Now, each argument is described in the information returned by NS_probdesc and this description can be translated into meaningful variable names in the user source code. For instance, X2 should be a pointer to the matrix of the linear system, and X3 should be an integer that is the leading dimension of the matrix. We can now move on to the descriptions of the different ways of calling NetSolve from C or Fortran77.