Homework 4 [2014] Discussion of solution¶

Sample solutions can be found in $UWHPSC/solutions/homework4.

Reminder to help debugging Fortran codes:

Use the compiler flag -g so that you can run the executable with GDB (or LLDB on Mac Mavericks), which might help determine where the code dies if it does, and can help in examining variables as it runs by setting breakpoints.
Additional compiler flags are very helpful, e.g. -fbounds-check to have it check array bounds, so that for example if x is dimensioned as x(0:10) and you try to access x(11) then it will give an error rather than taking whatever garbage is in the element of memory that this points to.
See Fortran debugging and Useful gfortran flags for more tips.

With the Makefiles we are using, you can set e.g.:

FFLAGS = -g -Wall -fbounds-check -ffpe-trap=zero,overflow,underflow,invalid

or even set these on the command line with something like:

$ make test1 -f Makefile1 FFLAGS="-g -Wall -fbounds-check"

Remember that to have these take effect you will have to remove all the old .o files first so that it recompiles the code rather than thinking they are up to date. You can do rm *.o or, if the Makefile is set up with a clean target, something like:
```
$ make clean -f Makefile1
```

Some common errors that people made:

Part 1

The most common error was blindly following the coarse grain example and dividing up n instead of n_samples between threads.
Incorrect OpenMP reductions.

Part 2