[Rd] calling Lapack and BLAS routines from C

[Prof Brian Ripley]

On Fri, 4 Sep 2009, Marcin Hitczenko wrote:

> Hi,
>
> I am working on a UNIX machine and I am interfacing R and C with the .C
> function. I am trying to call LAPACK and BLAS routines, but am running
> into a problem where, while I am able to run the BLAS routines, I cannot
> run the LAPACK routines.
>
> I compile my .c file (at end of email) in the following way:
>
> [mhitczen at jlogin2 ~/Cstuff]$ R CMD SHLIB testmore.c
>
> gcc -std=gnu99 -I/home/mhitczen/R-2.9.0/include  -I/usr/local/include
> -fpic  -g -O2 -c testmore.c -o testmore.o
> gcc -std=gnu99 -shared -L/usr/local/lib -o testmore.so testmore.o
>
> However, I get the following error in R:
>
>> dyn.load("testmore.so")
> Error in dyn.load("testmore.so") :
>  unable to load shared library '/home/mhitczen/Cstuff/testmore.so':
> /home/mhitczen/Cstuff/testmore.so: undefined symbol: dpotrf_
>
> This error goes away and everything works when I simply call the BLAS
> routine (In the testmore.c file I simply remove funct2, leaving funct
> which calls the routine "dgemm" found in the BLAS.h file).
>
> I read the "Writing R Extensions" and created a file:
> /R-2.9.0/src/Makevars that contains the line:
> PKG_LIBS = $(LAPACK_LIBS) $(BLAS_LIBS) $(FLIBS)

That is not where it tells you to put the file.  It needs to be in the 
direcctory where you run the compile (normally the 'src' directory of 
a package), and in your case that seems to be ~/Cstuff.

That BLAS works is fortuitous, depending on the way you built R.

[...]

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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