I've noticed that FriCAS doesn't have a numerical implementation of
polylog's yet.
So I will have to interface some C/Fortran code. For that I have
constructed a small
example:
test.c:
void testfun(double arg, double* realpart, double* imagpart)
{
*realpart = 1.0 * arg;
*imagpart = 3.14 * arg;
return;
}
gcc -shared -o libtest.so test.c
test.lsp:
(sb-alien:load-shared-object "./libtest.so")
(defun testfun (arg)
(sb-alien:with-alien ((repart (double-float) 0.0d0) (impart
(double-float) 0.0d0))
(sb-alien:alien-funcall
(sb-alien:extern-alien "testfun" (sb-alien:function sb-alien:void
(double-float) (* double-float) (* double-float)))
arg (sb-alien:addr repart) (sb-alien:addr impart)
)
(complex repart impart)
)
)
And I can successfully use that function within sbcl:
sbcl --load "test.lsp"
(testfun 10.0d0)
#C(10.0d0 31.400000000000002d0)
Within FriCAS I ran ")lisp (load "test.lsp")" and it
seems to parse/load the file successfully, but I can't directly use that
function, i.e. (testfun 10.0d0) within ")fin", and neither from within
FriCAS as TESTFUN(1$DoubleFloat)$Lisp:
debugger invoked on a TYPE-ERROR in thread
#<THREAD "main thread" RUNNING {1002410103}>:
The value
0.0d0
is not of type
(SB-ALIEN:ALIEN (* T))
from the function type declaration.
As it turns out, somehow I can not give it an initial value here, and I
just have to declare it with (repart (double-float)), which is fine, but I
am wondering why.
The final step for me is to convert the SExpression into a FriCAS
Complex(DoubleFloat). For that I looked into the SExpression domain, and it
seems to be easiest to instead return (list repart impart) and then have
something like:
testfun(xx) ==
res := TESTFUN(xx :: DoubleFloat)$Lisp
complex(float car res, float car cdr res)
Presumably I could convert this into Complex(DoubleFloat) within the Lisp
code directly with some SPADCALL calls? But the current way seems to be
perfectly fine, but I am wondering if this is the right/recommended way to
do it. Overall I'm really happy how easy this turned out to be.
Thanks,
Tobias
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