Lyons W.C. (ed.). Standard handbook of petroleum and natural gas engineering.2001- Volume 1
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Computer Applications
115
FORMAT
and
ENTRY
Statements
Data Structures.
IMPLICIT Statements
PARAMETER Statements
DIMENSION, COMMON TYPE,
and EQUIVALENCE Statements
Statement
Function
DATA Definitions
Executable
Statements
Statements
Variable-May be assigned value by a numerical or character constant, by
Array-May have up
to
seven dimensions; number and size (upper and lower
File-External (physical) only; may be sequential or random access.
input, or by an expression.
boundaries) of dimensions are declared in DIMENSION or TYPE statements.
Statements.
Most statements, except where noted otherwise, begin in the
seventh column of a page considered to be 80 columns wide;
continuation lines
are indicated by a
"+"
(symbol may vary with version of language) in the sixth
column. The first five columns are reserved for
labels
(line numbers), which are
only required if the line is referenced by another statement, and for
comment
lines,
which are determined by a character in the first column. Columns
7
to
72
are reserved for statements; 73-80 are not read. (See Table
1-24
for required
order of statements in FORTRAN.)
Nonexecutable Statements.
Program unit heading-Program name, function name, or subroutine name.
Type declaration-Specifies data type
to
be represented by a variable name
(overrides defaults), e.g.,
REAL MSR
INTEGER COUNT, PNUM, AP
LOGICAL TEST1
CHARACTER* 10 LNAME
Implicit declaration-Allows type specification for all names beginning with
the given first letter(s)
IMPLICIT DOUBLE PRECISION (A-Z)
IMPLICIT COMPLEX (C)
Table
1-24
Order
of
Statements in FORTRAN
I
PROGRAM,
FUNCTION,
SUBROUTINE
or
BLOCK
DATA
Statements
COMMENT
Lines
116
Mathematics
Dimension statement-Specifies number and size of dimensions for each array
(may be included in Type statement); lower bound default is 1
DIMENSION A1(5:10),A2( 15)
DIMENSION A3(0:5,0: 10,lO: 100),A4( 10,10,10,10)
or
INTEGER Al(5: 10),A2( 15)
Common statement-Defines a common block
of
global variables (one common
block may have
no
specified name)
COMMON/blockname/varnames/blockname/varnames
COMMON X,Y,Z/C2BLK/A,B,C
Data may be entered into variables declared in a labeled COMMON block by
an assignment
or
an input statement or through a BLOCK DATA subprogram
as defined in subprogram statements.
Equivalence statement-Assigns two or more variable names to the same
memory location
EQUIVALENCE(A,B,C)
Parameter statement-Declares the name of a constant whose value cannot
be changed in the program
PARAMETER name
End statement-Compiler signal for end of unit
END
Executable Statements
Assignment statements may be DATA statements and are used mainly
to
assign initial values
to
variables
DATA A,B,C,D,E/ 1. ,2
.,3.
,4. ,5./X,Y,Z/S
*
IO.
or
values assigned by numerical or character constants or by expressions (see
Table 1-25 for arithmetic operators and precedence)
PI
=
3.1415927
C1
=
‘This is a test’
X(1,J)
X(I
-
1J)
+
Y(J)*Z**3
Input/Output statements may be either list-directed (stream) or formatted.
List-directed
I/O
statements may be
READ(device#,*)varl,var2,
.
. .
WRITE(device#,*)varl,var2,
. .
.
PRINT
*
varl,var2,
.
. .
Computer Applications
117
Table
1-25
Precedence
of
FORTRAN
Operators
Class
Level Symbol
or
Mnemonic
EXPONENTIAL First
tt
ARITHMETIC
Second
Third
*,
1
Fourth
+,
-
-
(negation) and
+
(identity)
RE L AT
I
0
N A
L
Fifth
.GT.,.GE.,.LT.,.LE.,.EQ.,.NE
LOGICAL
Sixth .NOT.
Seventh .AND.
Eighth
.OR.
Ninth .EQV. ,.NEQV
where device# refers to either a device such as a screen or printer or to
a
disk
file. Usually the default input device (referenced by an asterisk rather than a
device#) is the keyboard and the default output device (also referenced by an
asterisk) is the screen. PRINT connects only
to
the printer. Other devices and
files may be assigned device numbers through file handling statements (see
later).
A
statement requesting list-directed input from the default device (the
keyboard) might be, for example,
READ( ",")TEMP,PRSSR,LENGTH
Formatted
1/0
statements
require edit specifiers (see Table 1-26 for list) for
each variable
to
be handled and may also include strings
of
characters enclosed
in single quote marks. The format may be given in a separate format statement
(referenced by a line number and labeled) or, in many systems, may be enclosed
in quotes and parentheses in the 1/0 statement itself. The general form for
formatted 1/0 statements is
READ(device#,label)varl,var2,
. . .
WRITE(device#,label)varl,var2,
.
.
.
PRINT label varl,varZ,
. . .
label FORMAT(1ist
of
specifications)
For example,
READ(
*,
lOO)X(
l),Y,I
100
FORMAT( lX,2F12.4,15)
WRITE(6,l lO)(TEMP(I),I
=
1,5)
110 FORMAT( lX,5(F7.3,2X))
WRITE(
*,'(
"TEMP AT SURFACE IS ",FS.S)')TSURF
File handling statements
allow the manipulation of sequential and random
access files. (Since there is considerable variation from one system to the next,
the following information is given in general terms only.) Devices are treated
118
Mathematics
Table
1-26
FORTRAN
Edit
Specifiers
A
D
E
F
G
H
I
L
P
S
SP
ss
TL
TR
X
I
BN
BZ
Integer
Real
Character
Exponential
Character data fields
Double precision data fields
Real data fields-exponential (E) notation
Real data fields-decimal notation
General form
Character constants
Integer data fields
Logical data fields
Scaie factors, used with
D,
E,
F. and G specifiers to shift the decimal
point or exponent size for output
Restores the optional
+
convention
to
the compiler
Prints
+
with all subsequent positive data
Suppresses
+
for all subsequent positive data
Next character will be inputloutput the specified number of spaces
left of the current position
Next character will be inpuffoutput the specified number of spaces
right of the current position
Skip the specified number of spaces before next character is inpuvoutput
Ends format control if no more data items in list
Skips a record
Specifiers for input operations only
Specifies that blank characters are to be ignored
Specifies blank characters are
to
be read as zeros
Specifications for time four most common data types
Iw
Fw.d
Aw
Ew.d
as sequential files, while disk files may be sequential or random access. The
following statements are generally accepted forms:
OPEN(1ist of specifiers)-Connects an existing file to an 1/0 device or generates
a new file, and specifies a device (unit) number. The specifiers (required and
optional) are:
UNIT
=
IOSTAT
FILE
ERR
STATUS
ACCESS
FORM
RECL
BLANK
file unit (device) number
integer variable for
I/O
status
name of file
label for error transfer
file status descriptor, may be OLD, NEW, SCRATCH,
or
UN-
KNOWN
may be SEQUENTIAL or DIRECT
may be FORMATTED or UNFORMATTED
record length, if file access is DIRECT
specifies blank handling, either NULL
or
ZERO
Computer Applications
119
CLOSE(1ist of specifiers)-Disconnects a file. The specifiers may be:
UNIT
=
IOSTAT as in OPEN
ERR as in OPEN
STATUS
INQUIRE(1ist of specifiers)-Returns information about the attributes
of
a file.
Besides the UNIT
=
,
IOSTAT and ERR specifiers, the following specifiers may
be included:
file unit (device) number
may be KEEP or DELETE
EXIST
OPENED
NUMBER
NAMED
NAME
FORM
RECL
NEXT REC
BLANK
returns .TRUE. if file exists, else .FALSE.
returns .TRUE. if open, else .FALSE.
returns number of connected device
returns .TRUE. or .FALSE.
returns name of file
returns FORMATTED or UNFORMATTED
returns record length in direct access file
returns number of next record in direct access file
returns whether blanks or zeros specified
The following statements must include the UNIT
=
and may include the IOSTAT
and/or the ERR specifiers:
REWIND(1ist of specifiers)
-
Causes a sequential file
to
be rewound
to
BACKSPACE(1ist of specifiers)
-
Causes a sequential file to rewind one record
ENDFILE(1ist of specifiers)
-
Places an end-of-file mark on a sequential
first record
file
A few examples of file-handling statements are:
OPEN(UN1T
=
6,IOSTAT
=
FSTAT,FILE
=
‘PRINTER’,STATUS
=
‘NEW’
OPEN(4,FILE
=
‘DATAl’,STATUS
=
‘OLD’)
CLOSE(6)
BACKSPACE(4,ERR
=
500)
For
Control statements
affect the flow of instructions within a program unit.
control between units, see subprogram statements later.) These may be general,
conditional, or iterative statements.
General control statements
are:
PAUSE n-Interrupts program run, resumption upon pressing “Enter”;
n
is
PAUSE ‘VALUE INVALID’
STOP n-Halts program run (n as above)
STOP 10050
GOTO i-Transfers control to statement labeled i, where
i
is an integer
GOTO 700
an optional character constant or integer of less than
5
digits, e.g.,
constant or variable with value of label, e.g.,
120
Mathematics
Conditional statements
are as follows:
IF(e)sl,sP,s3-Arithmetic
if, where e is an arithmetic expression and
sl,s2,s3
are statement labels; transfers control
to
a labeled statement depending on
whether e evaluates to a negative, zero, or positive value, respectively. For
example,
IF(I
-
5)
30,40,50
will transfer control to the statement labeled
40
if
I
=
5.
IF(e)st-Logical if, where
e
is a logical expression (see Table
1-26
for relational
and logical operators) and st is any executable statement except DO, IF, ELSEIF,
ENDIF, or END. For example,
IF(I.EQ.
1)
WRITE( *,*)‘YES’
IF(e) THEN-Block if, where e is a logical expression, followed by a sequence
of statements and completed by an ENDIF statement. The block may include
sub-blocks introduced by one or more ELSEIF statements and/or one ELSE
statement and all sub-blocks may contain nested IF-THEN-ELSE blocks within
them. For example,
IF(1.EQ.J) THEN
x=4
Y=5
ENDIF
IF( 1.EQ.J) THEN
ELSE
ENDIF
IF(1.EQ.J) THEN
x=4
x=5
x=4
ELSEIF(1.EQ.K) THEN
x=5
ELSE
ENDIF
The
iterative statement
in FORTRAN
is
the DO statement (although others
X=Y
may be constructed using conditional statements and GOTOs), where
DO st i
=
init,term,incr
introduces the repetitive section, and st
is
the label of the executable statement
marking the end of the loop (usually, but not necessarily, a CONTINUE state-
ment), i is the index or control integer variable and init, term, and incr
(optional) are the initial value for
i,
the terminal value for i, and the increment
of i
to
be used, respectively. These values must be integer constants, variables,
or expressions in standard FORTRAN
77,
but many extensions to the language
allow real values to be used. DO
loops
may be nested to a level determined by
a specific compiler. For example,
Computer Applications
121
DO 100 I
=
1,10,2
PR(1)
=
PPE(1
-
1)
100 CONTINUE
DO
100
I
=
lO,l,
-
1
DO 100
J
=
1,lO
100 ATR(1,J)
=
PU,I)*FRIC
DO
100
I
=
-
5,25,5
PF(1)
=
TFP(1)
-
FFG
IF(PF(I).GE.LMT) GOT0 110
100 CONTINUE
110 MAXC
=
I
Statement functions
are defined before any other executable statements in
the program and are called in the same way that subprogram or intrinsic
functions are called (see subprogram statements later). They are one-line
expressions that receive one or more parameters from the calling statement and
return a single calculated value to the function name in the calling statement.
For example, a statement function defined as
FDPT(X(I),Y(I),Z,I)
=
X(I)*Y(I)
+
Z**I
will calculate a value depending on the values of X(I),Y(I),Z, and
I
at the time
of
calling and return the calculated value to the calling statement through FDPT.
Subprogram statements
are those used to transfer control between program
units-the main program, functions, and subroutines. A
function
call
is performed
by invoking the name of the function module in an assignment statement, such as
X
=
FDPR(Z,Y(I))*PRF
which will transfer control to the function FDPR and pass the values
Z,
and
Y(1) to that unit. An intrinsic function or
a
statement function may be called
in the same way. (See Table 1-27 for a list of FORTRAN
77
intrinsic functions.)
A
subroutine
call
is performed by a statement such as
CALL
CALCSUB(MATFOR,I,J,PVAL)
which will transfer control to the subroutine CALCSUB and pass (and/or return)
the values MATFOR,I,J, and PVAL. A subroutine may have an ENTRY name
(parameter list) statement imbedded within it, which when called in the same
manner as the main subroutine call, will receive control transfer at that point.
Control passes from the called unit back to the calling unit when a RETURN
statement is encountered. Given a subroutine
Subroutine CALCSUB(MAT,M,N,Pl)
REAL MAT(
100)
P1
=
MAT(M)
+
MAT(N)
RETURN
ENTRY NEWCALC(MAT,M,N,P2)
P2
=
MAT(M)
+
MAT(N)
RETURN
END
122
Mathematics
Table
1-27
FORTRAN
Intrinsic Functions
Integer
IABS
IDlM
IDINT
IFlX
INT
ISlGN
MAX0
MAXI
MlNO
MIN1
MOD
ABS
ACOS
AIMAG
AlNT
ALOG
ALOG
10
AMAXl
AMlNl
AMOD
ANINT
ASlN
ATAN
ATAN2
cos
COSH
DIM
EXP
FLOAT
NlNT
REAL
SIGN
SIN
SlNH
SQRT
SNGL
TAN
TANH
DABS
DACOS
Returns the absolute value of an argument
Returns the positive difference between two arguments
Converts a double-precision argument to integer by truncation
Converts a real argument to integer by truncation
Truncates the decimal part of an argument
Transfers the sign from one integer argument
to
the other
Selects the largest value of several arguments
Selects the largest value of several -arguments, but converts any real
result to integer
Selects the smallest value of several arguments
Selects the smallest value of several arguments, but converts any real
result to integer
Returns the remainder from division of two arguments
Real
Returns the absolute value of an argument
Returns the arc cosine of an argument
Returns the imaginary part of a complex number
Truncates the decimal part of an argument
Returns the natural logarithm of an argument
Returns the common logarithm of an argument
Seiects the largest value
of
several arguments
Selects the smallest value of several arguments
Returns the remainder from division of two arguments
Returns the whole number nearest in value to the argument
Returns the arc sine
of
an argument
Returns the arc tangent of an argument
Returns the arc tangent
of
two arguments [arctan(a,/a,)]
Returns the cosine of an argument
Returns the hyperbolic cosine of an argument
Returns the positive difference between two arguments
Returns the exponential e raised to the power of the argument
Converts an argument to a real number
Returns the nearest integer value
Converts a complex argument
to
a real value
Transfers the sign from one argument to the other
Returns the sine of an argument
Returns the hyperbolic sine
of
an argument
Returns the square root of an argument
Converts a double precision argument to single precision
Returns the tangent of an argument
Returns the hyperbolic tangent of an argument
Double Precision
Returns the absolute value of an argument
Returns the arc cosine
of
an argument
Computer Applications
123
DASlN
DATAN
DATAN2
DBLE
DCOS
DCOSH
DDlM
DEXP
DINT
DLOG
DLOGlO
DMAX1
DMlNl
DMOD
DNINT
DPROD
DSlGN
DSlN
DSlNH
DSQRT
DTAN
DTANH
IDINT
CABS
ccos
CEXP
CLOG
CMPLX
CONJ
CSQRT
CSlN
Returns the arc sine
of
an argument
Returns the arc tangent of one argument
Returns the arc tangent of two arguments [arctan(a,/a,)]
Converts an argument
to
double precision
Returns the cosine of an argument
Returns the hyperbolic cosine
of an argument
Returns the positive difference between two arguments
Returns the exponential e raised
to
the power of the argument
Truncates the decimal part
of
an argument
Returns the natural logarithm
of
an argument
Returns the common logarithm of an argument
Selects the largest value of several arguments
Selects the smallest value of several arguments
Returns the remainder from division
of
two arguments
Returns the whole number ciosest in value
to
the argument
Converts the product of two real arguments
to
double precision
Transfers the sign from one argument to the other
Returns the sine of an argument
Returns the hyperbolic sine of an argument
Returns the square root of an argument
Returns the tangent of an argument
Returns the hyperbolic tangent
of
an argument
Converts the argument
to
the nearest integer value
Complex
Returns the absolute value
of
an argument
Returns the cosine of an angle
Returns the exponential e raised
to
the power of the argument
Returns the natural logarithm
of the argument
Converts the argument
to
a complex number
Returns the conjugate of a complex function
Returns the square root of an argument
Returns the sine of an argument-
a call
to
CALCSUB as before will return a value through
P1
to
PVAL and
a call
CALL NEW
C
ALC( MAT,
K,
L,PVAL)
will transfer control in at the ENTRY statement and return a value through
P2
to
PVAL. A BLOCK DATA subprogram enters data into the variables declared
in a labeled COMMON block and has the form
BLOCK DATA
(DATA, DIMENSION, IMPLICIT, TYPE, EQUIVALENCE,
COMMON and PARAMETER statements)
END
124
Mathematics
Pascal Language
Pascal names (of units, variables, array elements, etc.), consisting of an initial
letter followed by letters or digits, may be as long as needed in standard Pascal;
however, in practice, most compilers require that a name be unique within a
certain number of characters. (See Table
1-28
for reserved words which may not
be used as names.)
Data Types
(Data structures of all types, predefined and user-defined, must
be declared; see “Statements” for type declaration form.)
Integer-Predefined, scalar (ordered) type with a machine-dependent limit,
Real-Predefined scalar type, decimal, or scientific notation may be used.
Boolean-Predefined logical type, ordered
so
that false
<
true.
Char-Predefined character type, ordered by code. (See Table
1-22
for two
User-defined-See “Statements.”
predeclared as a constant
MAXINT.
common code sets.)
Data Structures
Constant-Type and value assigned at declaration, and once defined, neither
type nor value may be changed.
Variable-Type assigned at declaration and may not be changed; value assigned
by a numerical or character constant, by input or by an expression.
Array-May have more than one dimension; number of dimensions and type
are assigned at declaration and may not be changed; values are assigned to array
elements (which must be of same type) as they are to variables.
Packed array-Produces more efficient use of memory, but slower program
execution than a regular array.
Record-The elements (fields) may be of different types and may be accessed
at random; fields and their types are assigned at declaration and may not be
changed; field values are assigned as are variable values.
File-Composed of elements (which may be records or other data structures)
of the same type; sequential files only in standard Wirth Pascal; external
(physical) files (for input and output) must be declared with the program
heading (see “Statements”) and internal (temporary) files may be added for use
within the program; all files except INPUT and OUTPUT must be declared in
TYPE and/or
VAR
sections.
Set-Type must be ordinal; must be processed
as
whole (cannot be broken
down into elements).
Table
1-28
Pascal Reserved Words
and
array begin case
div
do downto
else
file for
function got0
in label mod
nil
of
or packed
procedure
record
repeat set
then
type
until
var while
const
end
if
not
program
to
with