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| -rw-r--r-- | fortran90.html.markdown (renamed from fortran95.html.markdown) | 124 |
1 files changed, 62 insertions, 62 deletions
diff --git a/fortran95.html.markdown b/fortran90.html.markdown index 5fa8ca88..2f2cfdfd 100644 --- a/fortran95.html.markdown +++ b/fortran90.html.markdown @@ -2,16 +2,16 @@ language: Fortran contributors: - ["Robert Steed", "https://github.com/robochat"] -filename: learnfortran.f95 +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 -versions are FORTRAN 77, Fortran 90, Fortran 95, Fortran 2003, Fortran 2008 and -Fortran 2015. +versions are FORTRAN 77, Fortran 90, Fortran 95, Fortran 2003, Fortran 2008, +Fortran 2015, and Fortran 2018. This overview will discuss the features of Fortran 95 since it is the most widely implemented of the more recent specifications and the later versions are @@ -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 '&' |