From help-octave-request at bevo dot che dot wisc dot edu  Tue Feb  8 02:41:44 2000
Subject: Re: Calling octave from within an external program
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: "Steven G. Johnson" <stevenj at alum dot mit dot edu>
Cc: piyush at its dot caltech dot edu, help-octave@bevo.che.wisc.edu
Date: Tue, 8 Feb 2000 02:42:33 -0600 (CST)

On  8-Feb-2000, Steven G. Johnson <stevenj at alum dot mit dot edu> wrote:

| > Maybe i just haven't looked at the right places but i'd like to call
| > some of the octave functions from C/C++ programs i have written.  I can
| > do this in matlab using their math libraries.  Does octave have an
| > equivalent.  If not, how would i do this?
| 
| I don't think Octave is designed for this (if it exists, that functionality
| is not documented).

You are right that it is not really documented, but it would not be
impossible to compile all of Octave except the main program into a
set of libraries (this is already done, octave.cc is the main program)
and then write a program that calls eval() or feval() from the library
to execute arbitrary Octave code.  I haven't actually tried doing this
myself, except with the main program for the Octave interpreter that
is defined in octave.cc.

| If you just want to use the matrix operations
| (multiply, invert, eigenvalues, etcetera), you might consider directly
| calling the same (free) libraries that Octave uses to implement its
| operations: BLAS and LAPACK.  See www.netlib.org/lapack for more info.

I find some advantage to having the C++ classes instead of calling
Lapack (for example) directly.  To me, something like

  Matrix A;

  // initialize elements of A somehow...

  SVD svd_of_A (A);

  cout << "U: " << svd_of_A.left_singular_matrix ();

  ...

is much simpler than the corresponding Fortran, which involves setting
up a workspace array of the right size, and calling a function
(dgesvd) that takes 14 parameters.

jwe



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