_preparation.qmd

# Preparation

## Exercise 0 -- getting on the same page

Before we start I want to be sure everyone has a working system.

As we move through the following exercise if you experience any issues please ask for
help and we will aim to sort you out before the main exercises.

\

:::{.fragment}
In terminal navigate to to the workshop directory, set up a python virtual environment
as you prefer, and install the workshop dependencies:

```default
python3 -m venv .venv
source .venv/bin/activate
pip install ./
```
:::

\

:::{.fragment}
Navigate to `exercises/exercise_00/` where you will see a python and
fortran code.
:::

## Python

`pytorchnet.py` defines a net `SimpleNet` that takes an input vector of length 5
and multiplies it by 2.

Note:

  - the `nn.Module` class
  - the `forward()` method

Running:
```default
python pytorch_net.py
```

should produce the output:
```default
Input is  tensor([0., 1., 2., 3., 4.]).
Output is tensor([0., 2., 4., 6., 8.]).
```


## Compilers and CMake

First we will check that we have Fortran, C and C++ compilers installed:

Running:
```default
gfortran --version
gcc --version
g++ --version
```
::::{.columns}
:::{.column width=60%}
Should produce output similar to:
```default
GNU Fortran (Homebrew GCC 14.1.0_1) 14.1.0
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.
```
:::
:::{.column width=40%}
and not:
```default
bash: command not found: gfortran
```
:::
::::

\

:::{.fragment}
::::{.columns}
:::{.column width=60%}
Later on we will also need CMake.
:::
:::{.column width=40%}
To check this is installed run:
```default
cmake --version
```
and verify it is >= 3.1.
:::
::::
:::

:::{.aside}
Check that gcc version is >= 9
:::

## Fortran

The file `hello_fortran.f90` contains a program to take an input array and call a
subroutine to multiply it by two before printing the result.

The subroutine is contained in a separate module `math_mod.f90`, however.

:::{.fragment}
We can compile both of these to produce `.o` object files and a `.mod` module files using:
```default
gfortran -c math_mod.f90 hello_fortran.f90
```
:::

:::{.fragment}
We then link these together into an executable `ftn_prog` using:
```default
gfortran -o ftn_prog hello_fortran.o math_mod.o
```
:::

:::{.fragment}
Running this as:
```default
./ftn_prog
```
should produce the output
```default
 Hello, World!
 Input:     0.00000000        1.00000000        2.00000000        3.00000000        4.00000000
 Output:    0.00000000        2.00000000        4.00000000        6.00000000        8.00000000
```
:::

:::{.aside}
object files contain code run by the machine, and module files contain interfaces to modules.
:::