Page 124 - Standard Handbook Of Petroleum & Natural Gas Engineering

Computer Applications 109

Problem Solving
The initial outline of a solution to a problem is the algorithm, i.e., a list of
English-language instructions with the following properties:

1. The execution of the proposed algorithm must be completed after a finite
number of operations, the number depending on the complexity of the
problem and the degree of detail of the algorithm.
2. The representation of the solution must have a unique interpretation,
computers having less tolerance for ambiguity than humans, so when
executing the steps with the same input data, the same outputs are obtained.
3. The algorithm must present the computer with sufficient information and
instructions to carry out the solution.
4. The scope of the algorithm may be predefined by the range of the inputs.

Programming Languages
A wide variety of programming languages are available ranging from machine
code, composed of sequences of 0’s and 1’s representing either data or instruc-
tions, which is completely processor dependent and not transferable, through
assembly languages consisting of mnemonics for instructions and usually hexa-
decimal representation of storage location addresses and of data to high-level
programming languages such as BASIC and FORTRAN. High-level languages may
be divided into procedure-oriented languages and problem-oriented languages.
The term problem-oriented languages should be read as “special-purpose
languages,” or “applications-oriented languages,” since in a more general context
all high-level languages may be used to solve problems. Some of these languages
have been designed for special applications such as electronic circuit analysis,
while others are more general purpose, such as those written for simulation or
statistical packages.
Procedure-oriented languages, so called because they allow the programmer
to concentrate on the process rather than on the machine architecture, include
familiar languages, such as FORTRAN, as well as many more recently developed
ones. Three of the high-level languages of common interest to engineers are:
1. BASIC: Beginners All Purpose Symbolic Instruction Code, most often an
interpreted (i.e., each line is translated into (object) machine code immediately
before execution and no object code is retained for future executions),
highly interactive language, with a minimum of imposed structure and the
ability to allow the user to access the memory and input/output hardware
of the machine. Its disadvantages are slow execution speed (although
compiled BASICs are frequently faster) and the great degree of programming
freedom, allowing users to create terrible messes if they so desire, with
little chance of error detection. Because of the great degree of variation
in BASIC implementations on different systems, it is necessary to refer to
a specific system manual for its BASIC syntax, as well as for the DOS (Disk
Operating System) instructions for that system, or to the BASIC texts in
the reference section for some general forms of the language.
2. FORTRAN: Formula Translating Language, the original, still most com-
monly used language for engineering computations. It is a compiled
language (the entire program is translated to object code and saved before
execution) that links to many libraries of subroutines and has a number
of special purpose extensions. FORTRAN has been much improved by the