differences for PR #29

Author: actions-user

02-variables.md

@@ -0,0 +1,101 @@
+---
+title: 'Logic'
+teaching: 15
+exercises: 15
+---
+
+::::::::::::::::::::::::::::::::::::: questions
+
+- How do we declare and assign values to variables?
+
+::::::::::::::::::::::::::::::::::::::::::::::::
+
+::::::::::::::::::::::::::::::::::::: objectives
+
+- Understand the different intrinsic data types.
+- Declare and assign variables and parameters.
+
+::::::::::::::::::::::::::::::::::::::::::::::::
+
+Fortran's `logical` type has two values:
+
+```fortran
+  logical :: is_below_20_metres = .false.
+  logical :: use_stochastic_physics = .true.
+```
+
+### Logical operators
+
+Values can be tested logical operators `.or.`, `.and.` and `.not.` are available, and 
+these can be used to set the value of logical variables. 
+
+The precedence is illustrated by, e.g.,
+```fortran
+  q = i .or. j .and. .not. k    ! evaluated as i .or. (j .and. (.not. k))
+```
+where q, i, j, and k are all logical variables.
+
+Use brackets to avoid confusion over operator precedence.
+
+### Relational operators
+
+To form logical expressions from numeric or other expressions, we require
+relational operators. The are two forms in Fortran, illustrated in the table
+below. It is recommended that you avoid the older form.
+
+| Relation                 | Operator | Older form | For              |
+|--------------------------|----------|------------|------------------|
+| Less than                | `< `     | `.lt.`     | `integer` `real` |
+| Less than or equal to    | `<=`     | `.le.`     | `integer` `real` |
+| Greater than             | `> `     | `.gt.`     | `integer` `real` |
+| Greater than or equal to | `>=`     | `.ge.`     | `integer` `real` |
+| Equal to                 | `==`     | `.eq.`     | `integer` `real` `complex`|
+| Not equal to             | `/=`     | `.neq.`    | `integer` `real` `complex`|
+
+### Logical equivalence
+
+Equivalence between two logical expressions or variables is established
+via the logical operators `.eqv.` and `.neqv.`. 
+
+While some some compilers may allow the use of `==`, this should be avoided.
+
+### Using logical operators
+
+These operators can be used to check and set the values of logical variables, dependent on other variables, e.g.
+```fortran
+program example4
+   implicit none
+
+   real, parameter    :: pi      = 3.14159265
+   logical, parameter :: switch1 = .true.
+
+   real    :: a=3.0
+   logical :: test1, test2, test3
+
+   test1 = a >= pi               ! True if a is greater than or equal to pi
+
+   test2 = (.not. test1)         ! True if test1 is False, False if test1 is True
+
+   test3 = (test2 .eqv. switch1) ! True if test2 is True, False if test2 is False
+
+   print *, test1
+
+   print *, test2
+
+   print *, test3
+
+end program example4
+```
+Compiling and running this code will give the following output
+```
+$  ./a.out 
+ F
+ T
+ T
+```
+
+:::::::::::::::::::::::::::::::::::::::: keypoints
+
+- Th
+
+::::::::::::::::::::::::::::::::::::::::::::::::::

03-maths.md

@@ -0,0 +1,26 @@
+---
+title: 'Strings'
+teaching: 15
+exercises: 15
+---
+
+::::::::::::::::::::::::::::::::::::: questions
+
+- How do we declare and assign values to variables?
+
+::::::::::::::::::::::::::::::::::::::::::::::::
+
+::::::::::::::::::::::::::::::::::::: objectives
+
+- Understand the different intrinsic data types.
+- Declare and assign variables and parameters.
+
+::::::::::::::::::::::::::::::::::::::::::::::::
+
+Variables store information we can use in our
+
+:::::::::::::::::::::::::::::::::::::::: keypoints
+
+- Th
+
+::::::::::::::::::::::::::::::::::::::::::::::::::

04-logic.md

@@ -60,7 +60,10 @@ contact: 'd.theodorakis@metoffice.gov.uk'
 
 # Order of episodes in your lesson
 episodes: 
-- introduction.Rmd
+- 02-variables.md
+- 03-maths.md
+- 04-logic.md
+- 05-strings.md
 
 # Information for Learners
 learners: 
@@ -78,4 +81,3 @@ profiles:
 sandpaper: astroDimitrios/sandpaper
 pegboard: astroDimitrios/pegboard
 varnish: astroDimitrios/varnish
-

05-strings.md

@@ -0,0 +1,20 @@
+---
+title: Discussion
+---
+
+## Frequently Asked Questions
+
+People often have questions about Fortran beyond the scope of the core material.
+Students who have completed episodes early
+might find value in looking through the following topics.
+
+Note that since this material isn't essential for most Fortran usage,
+it won't be covered by the instructor.
+
+## Floating point precision
+
+There is a great article
+[Examples of floating point problems](https://jvns.ca/blog/2023/01/13/examples-of-floating-point-problems/)
+by Julia Evans.
+The article outlines what floating points numbers are
+and common problems with precision.