Introduction to scientific programming in Earth's Sciences

1
Introduction to scientific programming in Earth's
Sciences
J.W. Goethe University. Frankfurt

• Dr Guillaume RICHARD
• Institüt für Geowissenchaften 1.232
• richard_at_geophysik.uni-frankfurt.de

2
Overview

• 12 x 45min Lectures / 45min training classes
  (praktical)
• Basics (Hardware, OS, editor, etc.. )
• Basics 2 (Linux commands, Compile,Visualize )
• Languages Fortran (FORmula TRANslation)
• Languages Fortran (2)
• Languages Fortran (3)
• Languages C/C
• Languages Matlab (1)
• Languages Matlab (2)
• Languages Maple
• Introduction to Finite difference / Finite Volume
  method
• Introduction to Finite difference / Finite Volume
  method (2)
• Introduction to Finite elements method

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L. 3 Fortran1. Basics
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Fortran Basics
Some History Fifty Years of Fortran

• FORTRAN, the first high level programming
  language, was announced to the computing world by
  John Backus and his team from IBM at the Western
  Joint Computer Conference held in Los Angeles,
  California in February 1957
• For an An IBM 704 mainframe to use in nuclear
  reactor design
• F66, F77, F88 (oupps F90), F95, F2003
• More information on the background and
  development of the FORTRAN I, II and III
  compilers can be found on the Computer History
  Museum website (http//community.computerhistory.o
  rg/scc/projects/FORTRAN/)

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Fortran Basics
Sayings from cards distributed at Pioneer Day. 25
years anniversary (1982)
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Fortran Basics

• Compilers
• g95 GNU Fortran 95 compiler (gcc)
• gfortran (supports OpenMP-Open Multi Processing )
• ifort (Intel fortran compiler)
• Silverfrost FTN95
• FORCE Project - Fortran Compiler and Editor. an
  IDE for Fortran 77 that integrates the GNU
  Fortran 77 compiler (g77).
• (http//www.thefreecountry.com/compilers/fortran.s
  html)

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Fortran Basics

• Program Structure
• A program starts with the keyword PROGRAM,
• followed by a program name,
• followed by the IMPLICIT NONE statement,
• followed my some specification statements,
• followed by the execution part,
• followed by a set of internal subprograms,
• followed by the keywords END PROGRAM and the
  program name.
• For improving readability, your program should
  (must) add comment lines.

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Fortran Basics

• Comments
• All characters following an exclamation mark, !,
  except in a character string, are commentary, and
  are ignored by the compiler.
• A blank line is also interpreted as a comment
  line.
• Continuation Lines
• a statement must start on a new line. If a
  statement is too long to fit on a line, it can be
  continued with
• Ex A 174.5 Year
• () Count / 100

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Fortran Basics

• Literal constants
• Fortran has five types of constants
• Integer a string of digits with an optional
  sign
• Real 2 representations,
• decimal A decimal point must be presented ( no
  commas). Can have an optional sign.
• exponential an integer or a real number in
  decimal representation (the mantissa or
  fractional part), followed by the letter E or e,
  followed by an integer (the exponent).
• Ex12.3456e2 1234.56

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Fortran Basics

• Literal constants (next)
• Complex We will see if we have time to cover it
• Logical True or False (more later)
• character string must be enclosed between
  double quotes or apostrophes (single quotes). The
  length of the string is the number of characters
  of its content
• Ex 'Bill 2' and "Bill 2" content Bill 2
  and length 7
• Ex "Newton's apple" or 'Newton'' apple'

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Fortran Basics

• Fortran Identifiers
• It has no more than 31 characters
• The first character must be a letter,
• The remaining characters, if any, may be letters,
  digits, or underscores
• Fortran identifiers are case insensitive. Except
  for strings
• Fortran does not have any reserved words.
  Keywords as END, PROGRAM, DO are perfectly legal
  Fortran identifiers. However, this is definitely
  not a good practice. Keywords are in upper case.

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Fortran Basics

• Variables and Their Types
• A variable can be considered as a box that is
  capable of holding a single value of certain type
  (i.e. memory space).
• INTEGER the variable is capable of holding an
  integer
• REAL capable of holding a real number
• COMPLEX capable of holding a complex number
• LOGICAL capable of holding a logical value (i.e.
  .TRUE. or .FALSE.)
• CHARACTER capable of holding a character string
  of certain length

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Fortran Basics

• Variable Declarations
• Declaring the type of a Fortran variable is done
  with type statements.
• Ex type-specifier list
• For CHARACTER. Since a string has a length
  attribute, a length value must be attached to
  character variable declarations.
• Ex CHARACTER(LEN1) letter, digit
• CHARACTER(1) letter, digit
• CHARACTER letter, digit
• CHARACTER(LEN10) letter, digit1
• CHARACTER(LEN) letter, digit

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Fortran Basics

• The PARAMETER Attribute
• To assign a name to a value
• Add PARAMETER in front of the double colon ()
  and use a comma to separate the type name (i.e.,
  REAL) and the word PARAMETER
• Following each name, one should add an equal sign
  () followed by an expression. The value of this
  expression is then assigned the indicated name.
• The name assigned to a value is not a variable.
• After assigning a name to a value, that name can
  be used in a program, even in subsequent type
  statements.
•    Ex REAL, PARAMETER PI3.141592,
  PI2PIPI
• CHARACTER(LEN4), PARAMETER City "LA"
• CHARACTER(LEN), PARAMETER Name 'Billy'

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Fortran Basics

• Variables Initialization
• Initially the content of a variable (or a box) is
  empty. Therefore, before one can use a variable,
  it must receive a value.
• The use of un-initialized variables may cause
  unexpected result.
• To put a value into a variable
• initializing it when the program is run
• Ex REAL Offset 0.1, Length 10.0
• using an assignment statement (more later)
• Ex length 3.
• reading a value from keyboard or other device
  with a READ statement. (more later)

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Fortran Basics

• The Assignment Statement
• variable expression
• To save the result of the expression to the right
  of the assignment operator to the variable on the
  left.
• The expression is evaluated first (more soon).
• If the type of the expression is identical to
  that of the variable, the result is saved in the
  variable.
• Otherwise, the result is converted to the type of
  the variable and saved there.
• CHARACTER assignment follows the rules stated in
  the discussion of the PARAMETER attribute.
• Exercise swaps the values in A and B, with the
  help of C.

INTEGER A 3, B 5, C C A A B B C
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Fortran Basics

• Arithmetic Operators
• Fortran has 4 types of operators
• Arithmetic , , /, , -
• Fortran has an exponential operator . Thus,
  raising X to the Y-th power is written as XY
• Relational lt, gt, lt, gt, ,/
• Logical .NOT., .AND., .OR., .EQV., .NEQV.
• Character
• Operators are evaluated from left to right
  (excepted the exponential ).
• Ex ABC is equal to A(BC)

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Fortran Basics

• Arithmetic Expressions Modes
• An arithmetic expression is an expression using
  an operator ( , -, , /, )
• Single mode expression all of whose operands
  are of the same type. The type of the result of
  an operation is identical to that of the
  operands.
• Ex 2 4 5 / 3 2
• Mixed mode INTEGER operands are always
  converted to REAL. The result of a mixed mode
  expression is of REAL type.

--gt 2 4 5 / 3 2 --gt 8 5 / 3 2 --gt
8 5 / 3 2 --gt 40 / 3 2 --gt 40 / 3
2 --gt 40 / 9 --gt 4

• In expression ab where a is REAL, the result is
  undefined if the value of a is negative.
• Ex -4.02 is defined with -16.0 as its result,
  while (-4.0)2 is undefined.

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Fortran Basics

• Arithmetic Expressions Modes
• Mixed mode examples
• 5 (11.0 - 5) 2 / 4 9
• 25.0 1 / 2 3.5 (1 / 3)

• 5 (11.0 - 5) 2 / 4 9?5 (11.0 - 5.0)
  2 / 4 9
• 5 (11.0 - 5.0) 2 / 4 9 ? 5 6.0 2 /
  4 9
• 5 6.0 2 / 4 9 ? 5 36.0 / 4 9 ? 5
  36.0 / 4 9
• 5.0 36.0 / 4 9 ? 5.0 36.0 / 4 9 ? 180.0
  / 4 9
• 180.0 / 4 9 ?180.0 / 4.0 9?180.0 / 4.0
  9
• 45.0 9 ? 45.0 9?45.0 9.0 ? 54.0

• ?25.0 1 / 2 3.5 (1 / 3)?25.0 / 2 3.5
  (1 / 3)
• 25.0 / 2 3.5 (1 / 3) ? 25.0 / 2.0 3.5
  (1 / 3)
• 12.5 3.5 (1 / 3) --gt 12.5 3.5 (1 /
  3)
• 12.5 3.5 0 --gt 12.5 3.5 0 --gt 12.5
  1.0 --gt 12.5

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Fortran Basics
CHARACTER Operator

• Only one character operator, the concatenation
  operator //
• Ex CHARACTER(LEN6)fn "Bob"4, ln"Marley",
  fulln11
• fullnfn//ln
• Substrings
• One can append the extent specifier at the end of
  a CHARACTER variable to indicate a substring.
• Ex ln(26) contains "arley", fn(2) contains
  "Bo
• fulln(24)ln(24) -gt fulln contains "BarlMarley "

FullN contains "Bob Marley "
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Fortran Basics
Exercises PROGRAM Fortran_Traps IMPLICIT
NONE INTEGER, PARAMETER A 2, B 2, H
3 INTEGER, PARAMETER O 4, P
6 CHARACTER(LEN5), PARAMETER M 'Smith', N
'TEXAS' CHARACTER(LEN4), PARAMETER X
'Smith CHARACTER(LEN6), PARAMETER Y
'TEXAS ! The exponential trap PRINT, "First,
the exponential trap " PRINT, A, ' ', B, '
', H, ' ', ABH PRINT, '( ', A, ' ',
B, ' ) ', H, ' ', (AB)H PRINT, A, '
( ', B, ' ', H, ' ) ', A(BH) PRINT, !
The integer division trap. Intrinsic function
REAL() converts ! an integer to a real
number PRINT, "Second, the integer division
trap " PRINT, PRINT, O, ' / ', P, ' ',
O/P PRINT, 'REAL( ', O, ' ) / ', P, ' ',
REAL(O)/P PRINT, O, ' / REAL( ', P, ' ) ',
O/REAL(P) PRINT, ! The string truncation
trap PRINT, "Third, the string truncation trap"
PRINT, 'IS ', M, ' STILL IN ', N, '?' PRINT,
'IS ', X, ' STILL IN ', Y, '? ' END PROGRAM
Fortran_Traps