Doesn’t have to use .pc - directly. But it has to be able to accept a user 
configuration one way or another. Using .pc to provide said configuration 
in a script is OK.
You might want to explore the way I did set up numpy in sage for example.

I looked at JAGS it takes --with-blas and —with-lapack options. You could 
solve your problem by doing
—with-lapack=-lopenblas 
or to keep with Volker spirit
—with-lapack=`pkg-cong —libs lapack`

Francois

> On 21/10/2016, at 21:14, Emmanuel Charpentier <emanuel.charpent...@gmail.com> 
> wrote:
> 
> While it is the "right" solution, it seems a bit heavy handed to ask all 
> authors of LAPACK-using programs susceptible to Sage's use to conform to the 
> convention suggested by Volker. This might not even be possible, depending on 
> system's infrastructure and source's configuration. And effectively forking 
> all such LAPACK-using programs puts an heavy load on the users...
> 
> Meanwhile, this trivial patch needs review.
> 
> HTH,
> 
> --
> Emmanuel Charpentier
> 
> Le vendredi 21 octobre 2016 00:17:11 UTC+2, François a écrit :
> I agree it would be best. Unfortunately it may not always be possible 
> to do that without heavy hacking. 
> Adding the liblapack link has trade-off, it would make some stuff work 
> out of the box but it could also hide problems on the long term. 
> 
> Really upstream of any project using blas/lapack needs to have a way 
> to check a user provided configuration before trying a automated detection 
> routine. Looking at you numpy (does the reverse by default without hacking, 
> look at user provided configuration only when its auto detection has failed). 
> 
> François 
> 
> > On 21/10/2016, at 11:08, Volker Braun <vbrau...@gmail.com> wrote: 
> > 
> > We do have a pc file so IMHO the best way is to rely on the output of 
> > 
> > $ pkg-config --cflags lapack 
> > -I/mnt/disk/home/release/Sage/local/include 
> > $ pkg-config --libs lapack 
> > -L/mnt/disk/home/release/Sage/local/lib -lopenblas 
> > 
> > 
> > 
> > On Thursday, October 20, 2016 at 11:12:43 PM UTC+2, François wrote: 
> > This is because automatic blas/lapack detection is a hopeless task. 
> > You should pass your lapack libraries to the configuration script. 
> > If you can’t, hack it. 
> > And now that we have switched to openblas, -lopenblas provides lapack. 
> > 
> > François 
> > 
> > > On 21/10/2016, at 10:04, Emmanuel Charpentier <emanuel.c...@gmail.com> 
> > > wrote: 
> > > 
> > > Something just changed in the Sage build process : as of 7.4, LAPACK is 
> > > no longer available to programs running in the Sage shell. 
> > > 
> > > Case in point : I want to install JAGS (an MCMC sampler), which is needed 
> > > by the rjags R package, of some use to Bayesian R users... This package 
> > > compiled fine in the Sage shell up to Sage 7.4beta6. Now, the --configure 
> > > step fails with : 
> > > 
> > > checking for cheev_ in -llapack... no 
> > > checking for cheev_ in -llapack_rs6k... no 
> > > configure: error: "You need to install the LAPACK library" 
> > > 
> > > Indeed : 
> > > 
> > > charpent@asus16-ec:~$ find /usr/local/sage-7/ -iname "*lapack*so*" 
> > > /usr/local/sage-7/local/lib/R/modules/lapack.so 
> > > /usr/local/sage-7/local/lib/python2.7/site-packages/cvxopt/lapack.so 
> > > /usr/local/sage-7/local/lib/python2.7/site-packages/numpy/linalg/lapack_lite.so
> > >  
> > > /usr/local/sage-7/local/lib/python2.7/site-packages/scipy/linalg/_flapack.so
> > >  
> > > /usr/local/sage-7/local/lib/python2.7/site-packages/scipy/linalg/cython_lapack.so
> > >  
> > > charpent@asus16-ec:~$ find /usr/local/sage-7/ -iname "*lapack*h*" 
> > > /usr/local/sage-7/local/lib/R/include/R_ext/Lapack.h 
> > > /usr/local/sage-7/local/include/lapacke_mangling.h 
> > > /usr/local/sage-7/local/include/linbox/algorithms/numeric-solver-lapack.h 
> > > /usr/local/sage-7/local/include/lapacke_config.h 
> > > /usr/local/sage-7/local/include/lapacke.h 
> > > 
> > > 
> > > Short of forcing the Sage build process to use the system's LAPACK (which 
> > > can be done but, as far as I know, is not recommended), I don't see how 
> > > to force the creation of this library and its header file. 
> > > 
> > > Note that could be useful to reduce overhead : R (standard package) 
> > > creates its own version (probably for lack of finding it at build 
> > > time...) ; it also exists in the python package cvxopt. 
> > > 
> > > 1) What do you think ? 
> > > 
> > > 2) Should a ticket be filed ? 
> > > 
> > > HTH, 
> > > 
> > > -- 
> > > Emmanuel Charpentier 
> > > 
> > > -- 
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