External Functions

1 General Description

It is possible to call functions defined outside the Modelica language. The body of an external function is marked with the keyword external possibly followed by any of he optional items language_spec, external_function_call_spec or external_function_annotation. If you just user the keyword external without any of the optional items a number of default rules apply, e.g. , if no external language is specified the implementation language for the function is assumed to be C.

(??Note- should also give examples of executable external calls)

2 Default Call

clear()

In the function log, the default mapping rules apply.

function log input Real x; output Real y; external; end log;

3 Specified Call

The leastSquares function uses an external function. Here the language is specified to be Fortran 77.

function leastSquares "Solves a linear least squares problem" input Real A[:,:]; input Real B[:,:]; output Real Ares[size(A,1),size(A,2)] := A; // Factorization is returned in Ares for later use output Real x[size(A,2), size(B,2)]; protected Integer lwork = min(size(A,1), size(A,2)) + max(max(size(A,1), size(A,2)), size(B,2))*32; Real work[lwork]; Integer info; String transposed = "NNNN"; // Workaround for passing character data to Fortran routine external "FORTRAN 77" dgels( transposed, 100, size(A,1), size(A,2), size(B,2), Ares, size(A,1), B, size(B,1), work, lwork, info ); end leastSquares;

4 A Large Example

The external function interface supports a number of advanced features such as in-out parameters and declaration of temporary work variables, which are illustrated by the following rather complicated example.

function BilinearSampling "Function for Discrete-time <--> continuous-time systems conversion by a bilinear transformation" input Real alpha := 1, beta := 1; input Real A[:, size(A, 1)], B[size(A, 1), :], C[:, size(A, 1)], D[size(C, 1), size(B, 2)]; input Boolean isContinuous := true; output Real Ares[size(A, 1), size(A, 2)] := A, // Ares is in-out to the Fortran function Bres[size(B, 1), size(B, 2)] := B, Cres[size(C, 1), size(C, 2)] := C, Dres[size(D, 1), size(D, 2)] := D; output Integer info; protected Integer iwork[size(A, 1)]; // Work arrays Real dwork[size(A, 1)]; String c2dstring := if isContinuous then "C" else "D"; external "FORTRAN 77" abo4md(c2dstring, size(A,1), size(B,2), size(C,1), alpha, beta, Ares, size(Ares, 1), Bres, size(Bres, 1), Cres, size(Cres, 1), Dres, size(Dres, 1), iwork, dwork, size(dwork, 1), info); end BilinearSampling;

The following Modelica class contains an example call to BilinearSampling, which via the external function interface is transformed to a call to ab04md.

class BilinearSamplingTest parameter Real alpha = 1, beta = 1; parameter Real A[:, :] = [0, 1; 2, 4], // Coefficients B[:, :] = [5, 6; 7, 8], C[:, :] = [9, 10; 11, 12], D[:, :] = [13, 14; 15, 16]; Real Ares [size(A, 1), size(A, 2)], Bres [size(B, 1), size(B, 2)], Cres [size(C, 1), size(C, 2)], Dres [size(D, 1), size(D, 2)]; Integer info; equation (Ares, Bres, Cres, Dres, info) = BilinearSampling(alpha, beta, A, B, C, D, true); end BilinearSamplingTest;