diff --git a/fortran90.html.markdown b/fortran90.html.markdown
index 4209d374..2f2cfdfd 100644
--- a/fortran90.html.markdown
+++ b/fortran90.html.markdown
@@ -5,8 +5,8 @@ contributors:
filename: learnfortran.f90
---
-Fortran is one of the oldest computer languages. It was developed in the 1950s
-by IBM for numeric calculations (Fortran is an abbreviation of "Formula
+Fortran is one of the oldest computer languages. It was developed in the 1950s
+by IBM for numeric calculations (Fortran is an abbreviation of "Formula
Translation"). Despite its age, it is still used for high-performance computing
such as weather prediction. However, the language has changed considerably over
the years, although mostly maintaining backwards compatibility; well known
@@ -30,29 +30,29 @@ program example !declare a program called example.
! Declaring Variables
! ===================
-
+
! All declarations must come before statements and expressions.
-
+
implicit none !prevents dynamic declaration of variables (recommended!)
! Implicit none must be redeclared in every function/program/module...
-
+
! IMPORTANT - Fortran is case insensitive.
real z
REAL Z2
- real :: v,x ! WARNING: default initial values are compiler dependent!
+ real :: v,x ! WARNING: default initial values are compiler dependent!
real :: a = 3, b=2E12, c = 0.01
integer :: i, j, k=1, m
real, parameter :: PI = 3.1415926535897931 !declare a constant.
logical :: y = .TRUE. , n = .FALSE. !boolean type.
complex :: w = (0,1) !sqrt(-1)
character (len=3) :: month !string of 3 characters.
-
+
real :: array(6) !declare an array of 6 reals.
real, dimension(4) :: arrayb !another way to declare an array.
integer :: arrayc(-10:10) !an array with a custom index.
real :: array2d(3,2) !multidimensional array.
-
+
! The '::' separators are not always necessary but are recommended.
! many other variable attributes also exist:
@@ -65,8 +65,8 @@ program example !declare a program called example.
! in functions since this automatically implies the 'save' attribute
! whereby values are saved between function calls. In general, separate
! declaration and initialisation code except for constants!
-
-
+
+
! Strings
! =======
@@ -75,7 +75,7 @@ program example !declare a program called example.
character (len = 30) :: str_b
character (len = *), parameter :: a_long_str = "This is a long string."
!can have automatic counting of length using (len=*) but only for constants.
-
+
str_b = a_str // " keyboard" !concatenate strings using // operator.
@@ -98,7 +98,7 @@ program example !declare a program called example.
! Other symbolic comparisons are < > <= >= == /=
b = 4
else if (z .GT. a) then !z greater than a
- ! Text equivalents to symbol operators are .LT. .GT. .LE. .GE. .EQ. .NE.
+ ! Text equivalents to symbol operators are .LT. .GT. .LE. .GE. .EQ. .NE.
b = 6
else if (z < a) then !'then' must be on this line.
b = 5 !execution block must be on a new line.
@@ -145,32 +145,32 @@ program example !declare a program called example.
cycle !jump to next loop iteration.
enddo
-
+
! Goto statement exists but it is heavily discouraged though.
- goto 10
+ goto 10
stop 1 !stops code immediately (returning specified condition code).
10 j = 201 !this line is labeled as line 10
-
-
+
+
! Arrays
! ======
array = (/1,2,3,4,5,6/)
array = [1,2,3,4,5,6] !using Fortran 2003 notation.
arrayb = [10.2,3e3,0.41,4e-5]
array2d = reshape([1.0,2.0,3.0,4.0,5.0,6.0], [3,2])
-
+
! Fortran array indexing starts from 1.
! (by default but can be defined differently for specific arrays).
v = array(1) !take first element of array.
v = array2d(2,2)
-
+
print *, array(3:5) !print all elements from 3rd to 5th (inclusive).
print *, array2d(1,:) !print first column of 2d array.
-
+
array = array*3 + 2 !can apply mathematical expressions to arrays.
array = array*array !array operations occur element-wise.
!array = array*array2d !these arrays would not be compatible.
-
+
! There are many built-in functions that operate on arrays.
c = dot_product(array,array) !this is the dot product.
! Use matmul() for matrix maths.
@@ -180,13 +180,13 @@ program example !declare a program called example.
c = size(array)
print *, shape(array)
m = count(array > 0)
-
+
! Loop over an array (could have used Product() function normally).
v = 1
do i = 1, size(array)
v = v*array(i)
end do
-
+
! Conditionally execute element-wise assignments.
array = [1,2,3,4,5,6]
where (array > 3)
@@ -196,30 +196,30 @@ program example !declare a program called example.
elsewhere
array = 0
end where
-
+
! Implied-DO loops are a compact way to create arrays.
array = [ (i, i = 1,6) ] !creates an array of [1,2,3,4,5,6]
array = [ (i, i = 1,12,2) ] !creates an array of [1,3,5,7,9,11]
array = [ (i**2, i = 1,6) ] !creates an array of [1,4,9,16,25,36]
array = [ (4,5, i = 1,3) ] !creates an array of [4,5,4,5,4,5]
-
+
! Input/Output
! ============
-
+
print *, b !print the variable 'b' to the command line
! We can format our printed output.
print "(I6)", 320 !prints ' 320'
- print "(I6.4)", 3 !prints ' 0003'
+ print "(I6.4)", 3 !prints ' 0003'
print "(F6.3)", 4.32 !prints ' 4.320'
-
- ! The letter indicates the expected type and the number afterwards gives
+
+ ! The letter indicates the expected type and the number afterwards gives
! the number of characters to use for printing the value.
- ! Letters can be I (integer), F (real), E (engineering format),
+ ! Letters can be I (integer), F (real), E (engineering format),
! L (logical), A (characters) ...
print "(I3)", 3200 !print '***' since the number doesn't fit.
-
+
! we can have multiple format specifications.
print "(I5,F6.2,E6.2)", 120, 43.41, 43.41
print "(3I5)", 10, 20, 30 !3 repeats of integers (field width = 5).
@@ -230,7 +230,7 @@ program example !declare a program called example.
read "(2F6.2)", v, x !read two numbers
! To read a file.
- open(unit=11, file="records.txt", status="old")
+ open(unit=11, file="records.txt", status="old")
! The file is referred to by a 'unit number', an integer that you pick in
! the range 9:99. Status can be one of {'old','replace','new'}.
read(unit=11, fmt="(3F10.2)") a, b, c
@@ -241,39 +241,39 @@ program example !declare a program called example.
write(12, "(F10.2,F10.2,F10.2)") c, b, a
close(12)
- ! There are more features available than discussed here and alternative
+ ! There are more features available than discussed here and alternative
! variants due to backwards compatibility with older Fortran versions.
-
-
+
+
! Built-in Functions
! ==================
! Fortran has around 200 functions/subroutines intrinsic to the language.
- ! Examples -
+ ! Examples -
call cpu_time(v) !sets 'v' to a time in seconds.
k = ior(i,j) !bitwise OR of 2 integers.
v = log10(x) !log base 10.
i = floor(b) !returns the closest integer less than or equal to x.
v = aimag(w) !imaginary part of a complex number.
-
+
! Functions & Subroutines
! =======================
-
+
! A subroutine runs some code on some input values and can cause
! side-effects or modify the input values.
-
+
call routine(a,c,v) !subroutine call.
-
+
! A function takes a list of input parameters and returns a single value.
- ! However the input parameters may still be modified and side effects
+ ! However the input parameters may still be modified and side effects
! executed.
-
+
m = func(3,2,k) !function call.
-
+
! Function calls can also be evoked within expressions.
- Print *, func2(3,2,k)
-
+ Print *, func2(3,2,k)
+
! A pure function is a function that doesn't modify its input parameters
! or cause any side-effects.
m = func3(3,2,k)
@@ -297,7 +297,7 @@ contains ! Zone for defining sub-programs internal to the program.
function func2(a,b,c) result(f) !return variable declared to be 'f'.
implicit none
- integer, intent(in) :: a,b !can declare and enforce that variables
+ integer, intent(in) :: a,b !can declare and enforce that variables
!are not modified by the function.
integer, intent(inout) :: c
integer :: f !function return type declared inside the function.
@@ -328,14 +328,14 @@ contains ! Zone for defining sub-programs internal to the program.
end program example ! End of Program Definition -----------------------
-! Functions and Subroutines declared externally to the program listing need
+! Functions and Subroutines declared externally to the program listing need
! to be declared to the program using an Interface declaration (even if they
! are in the same source file!) (see below). It is easier to define them within
! the 'contains' section of a module or program.
elemental real function func4(a) result(res)
! An elemental function is a Pure function that takes a scalar input variable
-! but can also be used on an array where it will be separately applied to all
+! but can also be used on an array where it will be separately applied to all
! of the elements of an array and return a new array.
real, intent(in) :: a
res = a**2 + 1.0
@@ -345,7 +345,7 @@ end function func4
! Modules
! =======
-! A module is a useful way to collect related declarations, functions and
+! A module is a useful way to collect related declarations, functions and
! subroutines together for reusability.
module fruit
@@ -358,7 +358,7 @@ end module fruit
module fruity
! Declarations must be in the order: modules, interfaces, variables.
! (can declare modules and interfaces in programs too).
-
+
use fruit, only: apple, pear ! use apple and pear from fruit module.
implicit none !comes after module imports.
@@ -367,7 +367,7 @@ module fruity
public :: apple,mycar,create_mycar
! Declare some variables/functions private to the module (redundant here).
private :: func4
-
+
! Interfaces
! ==========
! Explicitly declare an external function/procedure within the module
@@ -377,14 +377,14 @@ module fruity
real, intent(in) :: a
end function func4
end interface
-
+
! Overloaded functions can be defined using named interfaces.
interface myabs
! Can use 'module procedure' keyword to include functions already
! defined within the module.
module procedure real_abs, complex_abs
- end interface
-
+ end interface
+
! Derived Data Types
! ==================
! Can create custom structured data collections.
@@ -394,19 +394,19 @@ module fruity
real :: dimensions(3) !i.e. length-width-height (metres).
character :: colour
end type car
-
+
type(car) :: mycar !declare a variable of your custom type.
! See create_mycar() routine for usage.
-
+
! Note: There are no executable statements in modules.
-
+
contains
subroutine create_mycar(mycar)
! Demonstrates usage of a derived data type.
implicit none
type(car),intent(out) :: mycar
-
+
! Access type elements using '%' operator.
mycar%model = "Ford Prefect"
mycar%colour = 'r'
@@ -414,7 +414,7 @@ contains
mycar%dimensions(1) = 5.0 !default indexing starts from 1!
mycar%dimensions(2) = 3.0
mycar%dimensions(3) = 1.5
-
+
end subroutine
real function real_abs(x)
@@ -425,7 +425,7 @@ contains
real_abs = x
end if
end function real_abs
-
+
real function complex_abs(z)
complex :: z
! long lines can be continued using the continuation character '&'