NPDECODES

This repository contains the codes for the homework problems of the recurring course Numerical Methods for Partial Differential Equations at ETH Zurich. The course treats finite element methods (FEMs) using the C++ library LehrFEM++ and relies on the following material:

• lecture notes
• homework problems

Moreover, enrolled students can access the moodle page of the course.

Requirements

Currently, only UNIX based operating systems are supported. Moreover, you need to have the following installed on your machine:

• C++17 compiler (e.g. gcc, clang)
• CMake (at least VERSION 3.10)
• python3
• A reader for .vtk files (e.g. paraview)
• git (not strictly needed, you could also download the repo as .zip file)

Getting started

This section is suited only for your own computer. To build the codes on the student computers of ETH see below. Open a terminal and type

git clone [email protected]:erickschulz/NPDECODES.git
cd NPDECODES/
mkdir build
cd build/
cmake ..

This will install LehrFEM++ and its dependencies into a folder ~/.hunter/. To build a specific problem, say TestQuadratureRules, proceed as follows:

cd homeworks/TestQuadratureRules/
make

This will build from the source files in NPDECODES/homeworks/TestQuadratureRules/, where the subfolder mysolution/ contains templates to be changed by the students. Recompilation is done by invoking make again. The following executables are generated:

• ./TestQuadratureRules_mastersolution: Runs the mastersolution.
• ./TestQuadratureRules_test_mastersolution: Runs unit tests on all important functions of the mastersolution.
• ./TestQuadratureRules_mysolution: Runs the students code, i.e. the one in mysolution/.
• ./TestQuadratureRules_test_mysolution: Runs unit tests the students code, i.e. the one in mysolution/.

There is two folders called homeworks/. One contains the source files and one contains the executables:

.
├── build (was created by you)
│   ├── homeworks
│   :   ├── TestQuadratureRules
│       :   ├── TestQuadratureRules_mastersolution      (executable)
│           ├── TestQuadratureRules_mysolution          (executable)
│           ├── TestQuadratureRules_test_mastersolution (executable)
│           ├── TestQuadratureRules_test_mysolution     (executable)
│           :
│
├── homeworks
:   ├── TestQuadratureRules
    :   ├── mastersolution (folder containing source files)
        ├── mysolution     (folder containing source files, to be modified by you)
        ├── templates      (folder containing source files)
        :

On the student computers

LehrFEM++ is already installed on the linux student computers in the ETH main building. You can even use them remotely by typing in your terminal

ssh -X <nethz_username>@slab1.ethz.ch

where <nethz_username> has the be replaced by your ETH username. To set up your local repository on the student computers, type:

cd /tmp
git clone [email protected]:erickschulz/NPDECODES.git
mv NPDECODES ~
cd ~/NPDECODES
mkdir build
cd build
export HUNTER_ROOT=/opt/libs/NumPDE
cmake ..

The first four lines are due to limited resources on the student computers. Setting the environment variable HUNTER_ROOT tells CMake where to look for the preinstalled libraries. This environment variable is local to your terminal, i.e. has to be redefined if you start a new terminal. Apart from this, you can use the folder ~/NPDECODES in the same way you would for the approach in the previous section. However, you have only very little memory available on the student computers. We therefore recommend to only build one problem at a time.

FAQ

clang: error: unknown argument: '-fcoalesce-templates'

Mac users, after updating to macOS Catalina 10.15.4, are receiving this error. The workaround is as follows: Navigate your terminal into the folder NPDECODES/ and type:

brew install gcc@8    #install gcc version 8, needs brew to be installed first...
gcc-8 --version       #check if gcc-8 was installed properly
g++-8 --version       #check if g++-8 was installed properly
rm -rf build          #delete the old build folder
mkdir build           #recreate it

If this has succeeded, you need to build the codes using the gcc compiler by defining the environment variables CC and CXX. This is done by navigating a terminal into NPDECODES/build/ and running:

export CC=gcc-8
export CXX=g++-8
cmake ..

If the installation is successful, you can than build your codes using make as before. Note that the gcc version under OSX usulally just links to clang. However, the procedure above installs the actual gcc compiler.