Started on the Bunny Flux Minibook

learn/bunnyflux/index.md

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+
+---
+layout: book
+title: Bunny Flux
+permalink: /learn/bunnyflux
+---
+
+# Bunny Flux
+
+I once had a physics professor explain the term *flux* by drawing a field with
+bunnies in it, and then described the flux as number of bunnies entering and
+leaving the field. I was struck by the silliness of the term *Bunny Flux*, and
+now I want to actually compute the *Bunny Flux*.
+
+To compute the Bunny Flux, I will use Modern Fortran, the Fortran Package
+Manager, and the fortran-stdlib project. This is an intermediate level tutorial.
+I will assume you are familiar with the basics -- variables, types, loops,
+conditionals, etc. There are other excellent minibooks that go over those things.
+
+Let's get started!
+

learn/bunnyflux/setup.md

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+
+---
+layout: book
+title: Setting Up Bunny Flux
+permalink: /learn/bunnyflux/setup.md
+---
+
+# Setup
+
+Getting started is always the hardest part. Thankfully, this is made easier
+with the Fortran Package Manager. We can create our new project with
+
+```sh
+$ fpm new bunnyflux
+```
+
+fpm creates a new `bunnyflux` directory that looks like this:
+
+```
+bunnyflux/
+  app/
+    main.f90
+  src/
+    bunnyflux.f90
+  test/
+    check.f90
+  fpm.toml
+  README.md
+```
+
+A fpm package (which we just created) is comprised of a *library* and an
+*application*. The package also bundles any *tests* that ensure the correctness
+of the program.
+
+A *library* is a bundle of code that can be executed by the *application*, or by
+someone else who wants to use your package in their own project. Libraries can
+be static or dynamic. For this project we will be using the default, which is a
+static library. This has a `.a` extension on Linux and a `.lib` extension on
+Windows.
+
+Each directory that fpm created has a specific purpose. `src/` contains source
+files for the library. `app/` contains source files for the application, and
+`test/` holds source files for any tests.
+
+The `fpm.toml` file is used to describe the package to fpm so it can build it
+properly. 
+
+`README.md` is a markdown file, used to describe the package to the world. Some
+version control hosting sites, like Github or Gitlab, will display the contents
+of this file on their website in a nicely formatted way.
+
+fpm has also automatically initialized a git repository in the package directory.
+
+First things first, let's add a brief description to the `README.md` file:
+
+```markdown
+# Bunny Flux
+
+In which I make up a numerical method to solve a problem that no one cares
+about to demonstrate features of Modern Fortran! (Also, Bunnies!)
+```
+That's good enough for now. Now on to `fpm.toml`.  Let's fill in all the header information:
+
+```toml
+name = "Bunny Flux"
+version = "0.0.0"
+license = "mit"
+author = "Dalon Work"
+maintainer = "dwwork@gmail.com"
+copyright = "Copyright 2022, Dalon Work
+```
+
+fpm also lets us specify other packages that we want to use in our package. A
+dedicated team of individuals has created many excellent fpm packages that we
+can use, most importantly the 'fortran-stdlib' project. Bunny Flux will lean on this project, but first we have to tell fpm that we want to do that. At the bottom of 'fpm.toml' we can add the following lines:
+
+```toml
+[dependencies]
+stdlib.git = "https://github.com/fortran-lang/stdlib
+stdlib.branch = "stdlib-fpm"
+
+[dev-dependencies]
+stdlib.git = "https://github.com/fortran-lang/stdlib"
+stdlib.branch = "stdlib-fpm"
+```
+
+The first paragraph tells fpm that the Bunny Flux library and application will
+rely on stdlib, and the second paragraph does the same for the tests.  The
+first time we try to build, fpm will automatically download and build the
+stdlib package for us. If you've ever experienced the brain-fogging tedium of
+getting someone else's code to compile, this killer fpm feature is amazing.
+
+Now let's try a test build:
+
+```sh
+fpm build
+```
+
+Oh dear -- apparently it's not all rainbows and butterflies like I promised. I got an error while building stdlib:
+
+```
+build/dependencies/stdlib/src/stdlib_hash_64bit.f90:66:29:
+
+   66 |         pow64_over_phi = int(z'9E3779B97F4A7C15', int64)
+      |                             1
+Error: Arithmetic overflow converting INTEGER(16) to INTEGER(8) at (1). This check can be disabled with the option ‘-fno-range-check’
+compilation terminated due to -fmax-errors=1.
+<ERROR> Compilation failed for object " build_dependencies_stdlib_src_stdlib_hash_64bit.f90.o "
+<ERROR>stopping due to failed compilation
+STOP 1
+```
+
+After some investigation, turns out this is a gfortran bug in my version of
+gfortran on my Linux Mint system. (compilers aren't perfect!), and we can
+overcome it by adding the compile flag as suggested to our compile line.
+Let's try again:
+
+```sh
+fpm build --flag -fno-range-check
+```
+
+That worked! It downloaded and built everything. This is now a good point to create our first git commit.
+
+
+
+
+
+
+
+

learn/bunnyflux/tdd.md

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+
+---
+layout: book
+title: Test Driven Developme