2' BASIC FORTRAN

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2. BASIC FORTRAN

• ? VARIABLES CONSTANTS
• ? DATA TYPES
• ? OPERATIONS
• ? ASSIGNMENT
• ? I/O
• ? PROGRAMMING STYLE

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VARIABLES CONSTANTS

• Variables are locations in the computers memory
  in which variable information may be stored.
• Constants are locations in which information is
  stored which cannot be altered during the
  execution of the program.

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DATA TYPES

• Numerical Data Types
• INTEGER
• REAL
• COMPLEX
• Non numerical Data Types
• CHARACTER
• LOGICAL

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Integer Numbers

• An integer is a whole number (positive, negative,
  or zero) and does not contain commas or a decimal
  point.
• Examples 5 1024 -512
• a5 b1024 c-512
• Integer variable definition in F
• integer a,b,c

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Real Numbers

• A real constant must contain a decimal point, but
  no commas are allowed.
• Examples 5.125
• -0.0273
• 0.0571
• 6.5274684E3 (6.5274684X103)
• x5.125 y-0.0273 z0.0571
• Real variable definition in F
• real x,y,z

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Complex Numbers

• A complex number is represented as a pair of real
  (i.e., floating point) numbers.
• The first component of the pair represents the
  real part of the complex data object and the
  second represents the imaginary part.
• Example
• Z a i b Z (a,b)
• -34i
• complex z

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Character constants (strings)

• F character set
• A B C D E F G H I J K L M N O P Q R S T U V W X Y
  Z
• a b c d e f g h i j k l m n o p q r s t u w x y z
• 0 1 2 3 4 5 6 7 8 9
• ? - / ( ) , . lt gt ! ?
• where ? represents the space or blank character

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Character strings

• Character constants, also called strings, are
  sequences of
• symbols from the ANSI standard character set for
  Fortran.
• The number of character constants between double
  quotes is the length of constant
• For example
• abcD-12o (the length is 8)

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Names Declarations

• character (len3) schr
• schrend
• The character data does not contain any blanks,
• commas and slashes. A name may contain up
  to
• 31 letters, digits, and underscore characters.
• 2. The character data is within the single record
  or line.
• 3. The first non-blank character is not a
  quotation mark.
• 4. The leading characters are not numeric
  followed by an asterisk since this would be
  confused with the multiple data item form (nc).
• IMPORTANT keywords such as program, write, and
  end are not actually names

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Ellis and Philips, 1998, p59

• program character_example
• character (len3) string_1
• character (len4) string_2, string_3
• string_1End
• string_2string_1
• string_3Final
• print ,string_1,string_2,string_3
• end program character_example
• EndEnd Fina

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Ellis and Philips, 1998, p51

• program list_directed_input_example
• integer int_1,int_2,int_3
• real real_1, real_2,real_3
• ! initialize all variables
• int_1-1
• int_2-2
• int_3-3
• real_1-1.0
• real_2-2.0
• real_3-3.0
• ! read data
• read ,int_1,real_1,int_2,real_2,int_3,real_3
• !print new values
• print ,int_1,real_1,int_2,real_2,int_3,real_3
• end program list_directed_input_example

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• Input Output
• 1,2.3,4,5.6,7,8.9 1 2.300 4 5.600 7 8.900
• 9 8.7 6 5.4 3 2.1 9 8.700 6 5.400 3 2.100
• 1 2.3 1 2.300 4 5.600 7 8.900
• 4 5.6
• 7 8.9
• 9,,,5.4,,2.1 9 -1.000 -2 5.400 -3 2.100
• 1,2.3,4,5.6/ 1 2.300 4 5.600 -3 -3.000
• / -1 -1.000 -2 -2.000 -3 -3.000

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NAMED CONSTANTS

• real, parameter pi3.1415926, pi_by_twopi/2.0
• integer, parameter max_cases100

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Logical type An object of logical type has the
value true or false, or (0 or 1), or (yes or no)
Example Logical Circuits (Nyhoff and Leestma,
1992, p 108-109)

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• A and B are inputs.
• SUM and CARRY are outputs.
• AND gate An output pulse is produced only if
  there are pulses on both input lines.
• OR gate An output pulse is produced only if
  there is an input pulse on at least one of the
  input lines.
• NOT gate An output pulse is produced only when
  there is no incoming pulse.

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• False(F)0 (absence of pulse)
• True(T)1 (presence of pulse)
• SUM (A .OR. B) .AND. .NOT. (A .AND. B)
• CARRY A .AND. B
• A B CARRY SUM A B CARRY SUM
• 1 1 1 0 T T T F
• 1 0 0 1 T F F T
• 0 1 0 1 F T F T
• 0 0 0 0 F F F F

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ARITHMETIC OPERATORS IN F

• Operator Meaning
• addition
• - substraction
• multiplication
• / division
• exponentiation

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Arithmetic operator priorities

• Operator Priority
• High
• and / Medium
• and - Low

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• Example
• abcd/e-fg/hijk
• Steps
• temp_1fg
• temp_2cd
• temp_3temp_2/e
• temp_4temp_1/h
• temp_5ij
• temp_6btemp_3
• 7. temp_7temp_4temp_6
• temp_8temp_5temp_7
• 9. atemp_8k

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• Evaluation of the expression proceeds from left
  to right, within the priority level, except for
  exponentiation which is carried out from right to
  left, but may be altered by the use of
  parentheses.
• If one of the operands of an arithmetic operator
  is real, then the evaluation of that operation is
  carried out using real arithmetic, with any
  integer operand being converted to real.
• If an integer value is assigned to a real
  variable it is converted to its real equivalent
  before assignment if real value is assigned to
  an integer variable it is truncated before
  conversion to integer, and any fractional part is
  lost.

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MIXED MODE ASSIGNMENT

• Assume that b is a real variable whose value
  is 100.0, while c and d are integers having the
  values 9 and 10, respectively.
• a (bc)/d
• The result is 90.0
• a (c/d)b
• a gets 0 value.
• This phenomenon is known as integer division

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SIMPLE INPUT OUTPUT

• Read (unit , fmt ) Input List
• Write (unit , fmt ) Output List
• An asterisk as the unit in a read or write
  controls list designates
• the default input device (the keyboard) or the
  default output device
• (the terminal screen)
• An asterisk as the format designates
  list-directed formatting.
• Input data values for on-line list-directed input
  are entered at
• the computer keyboard in free form. Values must
  be separated by
• blanks.
• For example
• read (unit , fmt ) xval,yval,zval
• can be entered as
• 10.0 100.0 2.5

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Programming style

• Writing elegant programs requires
• ? Careful initial design
• ? Maintainability
• ? Portability (i.e. it can be compiled and
  executed on the other machines)

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Steps

• Goal of the program
• Explanations of inputs and outputs
• Clear design for the method
• Check for existing procedures libraries
• Use modular design (single block of code lt 50
  lines)
• Use descriptive names for variables and program
  units
• Perform as much as error checking on the input as
  is possible including for the different cases of
  the input variables
• Test the program by executing it

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A main program unit

• program name
• use statements
• .
• specification statements
• .
• executable statements
• .
• end program name

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A module program unit

• module name
• use statements
• .
• .
• specification statements
• end module name

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A module program unit containing procedure
definitions

• module name
• use statements
• .
• specification statements
• .
• contains
• procedure definitions
• .
• .
• end module name

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IN-CLASS PROBLEM SESSION -2

• Objective
• Learning Basic Fortran (data types, variables
• operations, etc.) Numerical methods
  (interpolation)
• Assignment
• In the following figure, moisture content of core
  samples (grams
• water/100g dried soils) is plotted as a function
  of depth (ft) given in the
• following Table. Write a program to calculate
  the moisture content at
• depth of 7.5 ft by using the following formula.
• Depth (ft) Moisture (grams water/100g dried
  solids)
• 0 124
• 5 78
• 10 54
• 15 35
• 20 30
• 25 21
• 30 22
• 35 18

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HOMEWORK

• Objective
• Learning Basic Fortran (data types, variables,
  operations,
• etc) Numerical methods (weighted average)
• Assignment
• Write a program to calculate a weighted average
  value of
• the shear wave velocities of three layered earth
  model and
• dominant resonance period of this model.
• The following formulas can be used
• V(h1v1h2v2h3v3)/(h1h2h3)
• T(4(h1h2h3))/V
• v1, v2, v3 shear wave velocities of layers
• h1, h2, h3 thicknesses of layers
• V weighted average value of shear wave
  velocities
• T resonance period
• v1100.0 m/s, v2200.0 m/s, v3300.0 m/s,
• h110.0 m, h220.0 m, h330.0 m