C interface

[jschueller]

This adds a C interface to the Fortran library thanks to the iso_c_binding module:

prima.h:

typedef void (*prima_function)(const double *x, double *f);
typedef void (*prima_function_con)(const double *x, double *f, double *con);

int prima_cobyla(prima_function_con calcfc, int n, int m, double *x, double rhobeg, double rhoend, int *maxfun, int iprint, void *state);
int prima_bobyqa(prima_function calfun, int n, double *x, double *xl, double *xu, double rhobeg, double rhoend, int *maxfun, int iprint, void *state);
int prima_newuoa(prima_function calfun, int n, double *x, double rhobeg, double rhoend, int *maxfun, int iprint, void *state);
int prima_uobyqa(prima_function calfun, int n, double *x, double rhobeg, double rhoend, int *maxfun, int iprint, void *state);

Some fortran modules have to be renamed to allow building everything into one single fortran library.

This also introduces a CMake build system to build both the Fortran library and the C library in a cross-platform manner.

Comments welcome

[github-advanced-security]

check-spelling found more than 10 potential problems in the proposed changes. Check the Files changed tab for more details.

[jschueller]

@zaikunzhang I think this is ready for review
I also want to add a data pointer & return code to the callback to allow user abort, but that would involve more modifications to the fortran side, so lets hear your thoughts on this before

[zaikunzhang]

@zaikunzhang I think this is ready for review

I also want to add a data pointer & return code to the callback to allow user abort, but that would involve more modifications to the fortran side, so lets hear your thoughts on this before

Dear @jschueller ,

Thank you very much for the wonderful contribution! Sorry for the slow response.

Is there a way to avoid renaming the Fortran files/subroutines, maybe by building the solvers one by one instead of all together?

Another monitor comment is that you may consider using https://github.com/marketplace/actions/setup-fortran to get Fortran compilers in CI.

Many thanks and best regards,
Zaikun

[jschueller]

While we could split the solvers, it would be impractical and also result in separate c libraries, this is probably not what we want because it would prevent to use more than one solver at at time in the client codes.
Also it speeds up compilation because common code does not need to be recompiled each time.

I will check out setup-fortran, thanks

[jschueller]

oh, yes, there are usually no subdirs under /lib, or at least its less frequent

[zaikunzhang]

• the external example is mostly there to provides the CMakeLists needed to use prima from another cmake projects, as opposed to the other "builtin" examples that are built from the same prima cmake project

Sorry, I still do not get the difference. What if we regard all examples under c/examples/ and fortran/example/ as external?

What about this one?

[zaikunzhang]

https://github.com/jschueller/prima/blob/97e9903f0662c0ce70dd9b96da763f497c578359/c/tests/t_large.c#L43-L47

What is this piece of code for?

[zaikunzhang]

5. Do you really intend to run the test every 5 minutes?

8. I do not think it is a good idea to print cstrv for unconstrained problems.

Any comments?

[zaikunzhang]

Could you direct me to the most recent run of the stress test? I have not found tests that run several hours and get cancelled by GitHub.

it should normally run 6 hours before it is canceled by GitHub. See https://github.com/orgs/community/discussions/58716#discussioncomment-6274151 for how to mark such workflows as successful.

Did you need this? Without doing so, the workflow will always be marked as a failure.

Thanks.

[jschueller]

• there is no difference in the C code itself, but examples from c/examples/ and fortran/example/ are already part of the build system of prima (built by the root CMakeLists), so they are not fully independent of prima in that regard (unless you copy the CMakeLists of the external example or write your own makefile of course), one can argue that the external folder is mainly there to showcase how to write an CMakeLists of a new project that links against prima
• it is there for instrumentation purpose; I wanted to see how many iterations I could allow before the 6h timeout,
  it could also be useful to tell if the code makes progress and is not frozen
• I modified the code to run it once every week no every 5 minutes of course
• I think we can keep the output cstrv, it will be zero in these cases, no big deal
• cron jobs will not be run until it is part of the default branch, so until merging

[zaikunzhang]

• one can argue that the external folder is mainly there to showcase how to write an CMakeLists of a new project that links against prima

For me, every example is to showcase how to use prima, as suggested by the word "example". That's why I suggest treating all examples as "external examples". This aligns with what I mentioned earlier:

#28 (comment)
#28 (comment)

[zaikunzhang]

• it is there for instrumentation purpose; I wanted to see how many iterations I could allow before the 6h timeout,
  it could also be useful to tell if the code makes progress and is not frozen

I suppose this is not needed.

[jschueller]

• ok, lets treat all as external
• lets make that an optional debug option then

[zaikunzhang]

Hi @jschueller ,

I tried the following.

git clone git@github.com:jschueller/prima.git -b cport
cd prima
cmake -S . -B . -DCMAKE_INSTALL_PREFIX=install
cmake --build . --target install
cd c/examples/cobyla
cmake -S . -B build -DCMAKE_INSTALL_PREFIX=install -DPRIMA_DIR=$PWD/../../../install/lib/cmake/prima/
cmake --build build --target install

Then, under c/examples/cobyla/install, there was program. However, when I tried

./program

I got the following:

./program: error while loading shared libraries: libprimac.so: cannot open shared object file: No such file or directory

I confirmed that libprimac.so is under /prima/install/lib.

Did I overlook something?

BTW, I understand it is easier to call the binary program, but it might be better to be called cobyla_example in this case.

Thank you.

[jschueller]

you might want to either set the environment variable LD_LIBRARY_PATH to the path of libprimac.so, or pass -DBUILD_SHARED_LIBS=OFF when configuring prima with cmake
it is also possible to set an rpath with cmake with CMAKE_INSTALL_RPATH, but it would require to set them at both levels

lets advise to build static libs from the README, that would be the easiest way

[zaikunzhang]

The new code in README works. Great!

1. Could we change the name of the binary to *a_example?
2. Should we / is it common to run the binary after it is compiled?
3. In the Fortran case, a mod subfolder is created under fortran/example/cobyla/install. It is empty. Is it standard to keep this directory? If no, could we avoid producing it?

Thanks.

[jschueller]

1. ok
2. ok
3. that should not happen with a build folder different than the source folder, I updated the README to put everything in /build

[zaikunzhang]

1. ok
2. ok
3. that should not happen with a build folder different than the source folder, I updated the README to put everything in /build

I really appreciate your quick action. Thank you very much.

1 is fixed on my side. Have you pushed the changes for 2 and 3? I do not see changes in the behavior.

[zaikunzhang]

a mod subfolder is created under fortran/example/cobyla/install.

Sorry, this is wrong. It is under fortran/example/cobyla.

[jschueller]

yes, it should not get created anymore with the new README

[zaikunzhang]

Merged! Thank you very much @jschueller !

Some links are broken in REAMDE. I will fix them.

[zaikunzhang]

Hi @jschueller , I modified the README after the merge, particularly the Modern Fortran and C sections. Do they look correct to you?

In particular, are these correct, especially the location of compiled files?

prima/README.md

Lines 214 to 215 in 9e19a7d

	This should create the **`primaf`** library for Fortran usage, located in the `install/lib` directory
	to be used with the module files in `install/include/prima/mod`.

prima/README.md

Line 231 in 9e19a7d

which should also create the **`primac`** library for C compilation, located in `install/lib` to be used with the **`prima.h`** header in `install/include/prima`.

Thanks.

[jschueller]

I believe so

[zaikunzhang]

Thank you! @jschueller

[zaikunzhang]

An announcement is made at
https://fortran-lang.discourse.group/t/prima-cmake-building-system-and-c-interface-available/6499/2
and
https://news.ycombinator.com/newest