Fortran tutorial pdf free download

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Computers are everywhere in our daily lives. Between the desktop, laptop, phone, bank, and vehicle, it is difficult to completely get away from computers. It only makes sense to learn a little about how a computer really works. This introduction is geared for non-computer science majors. The primary focus is on an introduction to problem solving and algorithm development. Preview the PDF. You do not have to register for expensive classes and travel from one part of town to another to take classes.

All you need to do is download the course and open the PDF file. This specific program is classified in the Computer programming category where you can find some other similar courses. Thanks to people like you? Note: Fortran 90 allows variable names of arbitrary length. Fortran 77 does not distinguish between upper and lower case, in fact, it assumes all input is upper case.

However, nearly all Fortran 77 compilers will accept lower case. If you should ever encounter a Fortran 77 compiler that insists on upper case it is usually easy to convert the source code to all upper case. Types and declarations Every variable should be defined in a declaration. This establishes the type of the variable. The most common declarations are:. Geoffrey Fox. Translation issues are identified, approaches are presented, a URL is provided for interested readers to download the package, and some unsolved problems are brought up.

Son Truong Cong Hoang. Lucy Smedstad. Robert Ribando. Onur Kamertay. Ojukwu Festus. Ahmed Alshnshory. Log in with Facebook Log in with Google. Remember me on this computer. Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. Download Free PDF. Related Papers. A prototype Fortran-to-Java converter. Introduction to Programing with Fortran1. Transitioning to Fortran 90 for Scientific and Engineering Calculations.

Preface The goal of this Fortran tutorial is to give a quick introduction to the most common features of the Fortran 77 programming language. It is not a complete reference! Many details have been omitted. The presentation focuses on scientific computations, mainly linear algebra. The outline of this tutorial was inspired by the excellent book "Handbook for Matrix Computations" by T.

Coleman and C. Permission to use this tutorial for educational and other non-commercial purposes is granted provided all author and copyright information is retained. Erik Boman, Stanford, December What is Fortran? Fortran is a general purpose programming language, mainly intended for mathematical computations in e.

However, following the current trend to only capitalize the first letter in acronyms, we will call it Fortran. Fortran was the first ever high-level programming languages. The work on Fortran started in the 's at IBM and there have been many versions since. By convention, a Fortran version is denoted by the last two digits of the year the standard was proposed.

There are also several versions of Fortran aimed at parallel computers. Users should be aware that most Fortran 77 compilers allow a superset of Fortran 77, i. Why learn Fortran? Fortran is the dominant programming language used in engineering applications. It is therefore important for engineering graduates to be able to read and modify Fortran code.

From time to time, so-called experts predict that Fortran will rapidly fade in popularity and soon become extinct. These predictions have always failed. One of the main reasons Fortran has survived and will survive is software inertia. Once a company has spent many man-years and perhaps millions of dollars on a software product, it is unlikely to try to translate the software to a different language.

Reliable software translation is a very difficult task. Consequently, if your program is written in ANSI Fortran 77 then it will run on any computer that has a Fortran 77 compiler. Thus, Fortran programs are portable across machine platforms. If you want to read some Fortran Standards Documents, click here.

Fortran 77 Basics A Fortran program is just a sequence of lines of text. The text has to follow a certain syntax to be a valid Fortran program. We start by looking at a simple example: program circle real r, area c This program reads a real number r and prints c the area of a circle with radius r.

Originally, all Fortran programs had to be written in all upper-case letters. Most people now write lower-case since this is more legible, and so will we. Program organization A Fortran program generally consists of a main program or driver and possibly several subprograms or procedures or subroutines. For now we will assume all the statements are in the main program; subprograms will be treated later. The stop statement is optional and may seem superfluous since the program will stop when it reaches the end anyways, but it is recommended to always terminate a program with the stop statement to emphasize that the execution flow stops there.

Column position rules Fortran 77 is not a free-format language, but has a very strict set of rules for how the source code should be formatted. The most important rules are the column position rules: Col.

Note that Fortran 90 allows free format. Comments A line that begins with the letter "c" or an asterisk in the first column is a comment. Comments may appear anywhere in the program.

Well-written comments are crucial to program readibility. You may also encounter Fortran programs that use the exclamation mark! This is highly non-standard in Fortran 77, but is allowed in Fortran The exclamation mark may appear anywhere on a line except in positions Continuation Occasionly, a statement does not fit into one single line.

One can then break the statement into two or more lines, and use the continuation mark in position 6. Example: c This demonstrates column position!

It is considered good programming style to use either the plus sign, an ampersand, or numbers 2 for the second line, 3 for the third, and so on. Blank spaces Blank spaces are ignored in Fortran So if you remove all blanks in a Fortran 77 program, the program is still syntactilly correct but almost unreadable for humans. The most common declarations are: integer list of variables real list of variables double precision list of variables complex list of variables logical list of variables character list of variables The list of variables should consist of variable names separated by commas.

Each variable should be declared exactly once. If a variable is undeclared, Fortran 77 uses a set of implicit rules to establish the type. This means all variables starting with the letters i-n are integers and all others are real. Many old Fortran 77 programs uses these implicit rules, but you should not! The probability of errors in your program grows dramatically if you do not consistently declare your variables. Integers and floating point variables Fortran 77 has only one type for integer variables.

Integers are usually stored as 32 bits 4 bytes variables. Fortran 77 has two different types for floating point variables, called real and double precision. While real is often adequat, some numerical calculations need very high precision and double precision should be used. Usually a real is a 4 byte variable and the double precision is 8 bytes, but this is machine dependent.

The parameter statement Some constants appear many times in a program. It is then often desirable to define them only once, in the beginning of the program. This is what the parameter statement is for. It also makes programs more readable. Expressions and assignment Constants The simplest form of an expression is a constant. There are 6 types of constants, corresponding to the 6 data types.

Hence, 2. For constants that are larger than the largest real allowed, or that requires high precision, double precision should be used. The notation is the same as for real constants except the "E" is replaced by a "D".

Examples: 2. The next type is complex constants. This is designated by a pair of constants integer or real , separated by a comma and enclosed in parantheses. Examples are: 2, -3 1. The fifth type is logical constants. These can only have one of two values:. Note that the dots enclosing the letters are required.

The last type is character constants. These are most often used as an array of characters, called a string. These consist of an arbitrary sequence of characters enclosed in apostrophes single quotes : 'ABC' 'Anything goes! A problem arises if you want to have an apostrophe in the string itself. If you want to change the default evaluation order, you can use parentheses. The above operators are all binary operators. Extreme caution must be taken when using the division operator, which has a quite different meaning for integers and reals.

If the operands are both integers, an integer division is performed, otherwise a real arithmetic division is performed. The expression on the right may contain other variables, but these never change value!

Type conversion When different data types occur in the same expression, type conversion has to take place, either explicitly or implicitly. Fortran will do some type conversion implicitly. However, in more complicated expressions, it is good programming practice to force the necessary type conversions explicitly.

For numbers, the following functions are available: int real dble ichar char The first three have the obvious meaning. Logical expressions Logical expressions can only have the value. A logical expression can be formed by comparing arithmetic expressions using the following relational operators:. Such symbols are allowed in Fortran 90, though. Logical expressions can be combined by the logical operators.

Logical variables and assignment Truth values can be stored in logical variables. The assignment is analagous to the arithmetic assignment. The rule is that arithmetic expressions are evaluated first, then relational operators, and finally logical operators. Hence b will be assigned. Logical variables are seldom used in Fortran. But logical expressions are frequently used in conditional statements like the if statement.

The if statements An important part of any programming language are the conditional statements. The most common such statement in Fortran is the ifstatement, which actually has several forms. The simplest one is the logical if statement: if logical expression executable statement This has to be written on one line. This example finds the absolute value of x: if x. The conditional expressions are evaluated in sequence until one is found to be true.

Then the associated code is executed and the control jumps to the next statement after the endif. Nested if statements if statements can be nested in several levels. Here is an example: if x. Loops For repeated execution of similar things, loops are used.

If you are familiar with other programming languages you have probably heard about for-loops, while-loops, and until-loops. Fortran 77 has only one loop construct, called the do-loop. The do-loop corresponds to what is known as a for-loop in other languages. Other loop constructs have to be simulated using the if and goto statements.

Typically, there will be many loops and other statements in a single program that require a statement label. The programmer is responsible for assigning a unique number to each label in each program or subprogram. Recall that column positions are reserved for statement labels. The numerical value of statement labels have no significance, so any integer numbers can be used. Typically, most programmers increment labels by 10 at a time. The variable defined in the do-statement is incremented by 1 by default.

However, you can define any other integer to be the step. Note: The do-loop variable must never be changed by other statements within the loop! This will cause great confusion. Many Fortran 77 compilers allow do-loops to be closed by the enddo statement. The advantage of this is that the statement label can then be omitted since it is assumed that an enddo closes the nearest previous do statement.

The pseudocode looks like this: do statements until logical expr Again, this should be implemented in Fortran 77 by using if and goto: label continue statements if logical expr goto label Note that the logical expression in the latter version should be the negation of the expression given in the pseudocode!

Loops in Fortran 90 Fortran 90 has adopted the do-enddo construct as its loop construct. Arrays Many scientific computations use vectors and matrices. The data type Fortran uses for representing such objects is the array. A one-dimensional array corresponds to a vector, while a two-dimensional array corresponds to a matrix. To fully understand how this works in Fortran 77, you will have to know not only the syntax for usage, but also how these objects are stored in memory in Fortran One-dimensional arrays The simplest array is the one-dimensional array, which is just a linear sequence of elements stored consecutively in memory.

For example, the declaration real a 20 declares a as a real array of length That is, a consists of 20 real numbers stored contiguously in memory. By convention, Fortran arrays are indexed from 1 and up. Thus the first number in the array is denoted by a 1 and the last by a However, you may define an arbitrary index range for your arrays using the following syntax: real b , weird Here, b is exactly similar to a from the previous example, except the index runs from 0 through The type of an array element can be any of the basic data types.

Examples: integer i 10 logical aa double precision x Each element of an array can be thought of as a separate variable. You reference the i'th element of array a by a i. This is the responsibility of the programmer, and the Fortran compiler will not detect any such bugs! Two-dimensional arrays Matrices are very important in linear algebra. Matrices are usually represented by two- dimensional arrays.

It is useful to think of the first index as the row index, and the second as the column index. Hence we get the graphical picture: 1,1 1,2 1,3 1,4 1,5 2,1 2,2 2,3 2,4 2,5 3,1 3,2 3,3 3,4 3,5 Two-dimensional arrays may also have indices in an arbitrary defined range.

This is because Fortran does not have dynamic storage allocation. This is perfectly legal. Example: real A 3,5 integer i,j c c We will only use the upper 3 by 3 part of this array.

Do not assume these elements are initialized to zero by the compiler some compilers will do this, but not all. Storage format for 2-dimensional arrays Fortran stores higher dimensional arrays as a contiguos linear sequence of elements. It is important to know that 2-dimensional arrays are stored by column.

So in the above example, array element 1,2 will follow element 3,1. Consider again the example where we only use the upper 3 by 3 submatrix of the 3 by 5 array A 3,5. The 9 interesting elements will then be stored in the first nine memory locations, while the last six are not used. This works out neatly because the leading dimension is the same for both the array and the matrix we store in the array. However, frequently the leading dimension of the array will be larger than the first dimension of the matrix.

Then the matrix will not be stored contiguously in memory, even if the array is contiguous. For example, suppose the declaration was A 5,3 instead. Then there would be two "unused" memory cells between the end of one column and the beginning of the next column again we are assuming the matrix is 3 by 3. This may seem complicated, but actually it is quite simple when you get used to it. If you are in doubt, it can be useful to look at how the address of an array element is computed.

Each array will have some memory address assigned to the beginning of the array, that is element 1,1. Note that lda is in general different from the actual matrix dimension.

Many Fortran errors are caused by this, so it is very important you understand the distinction! Multi-dimensional arrays Fortran 77 allows arrays of up to seven dimensions.

The syntax and storage format are analogous to the two-dimensional case, so we will not spend time on this. The dimension statement There is an alternate way to declare arrays in Fortran The statements real A, x dimension x 50 dimension A 10,20 are equivalent to real A 10,20 , x 50 This dimension statement is considered old-fashioned style today.

Subprograms When a programs is more than a few hundred lines long, it gets hard to follow. Fortran codes that solve real engineering problems often have tens of thousands of lines. The only way to handle such big codes, is to use a modular approach and split the program into many separate smaller units called subprograms. A subprogram is a small piece of code that solves a well defined subproblem. In a large program, one often has to solve the same subproblems with many different data. Instead of replicating code, these tasks should be solved by subprograms.

The same subprogram can be invoked many times with different input data. Fortran has two different types of subprograms, called functions and subroutines. Functions Fortran functions are quite similar to mathematical functions: They both take a set of input arguments parameters and return a value of some type. In the preceding discussion we talked about user defined subprograms.

Fortran 77 also has some built-in functions. There are many built-in functions in Fortran Some of the most common are: abs absolute value min minimum value max maximum value sqrt square root sin sine cos cosine tan tangent atan arctangent exp exponential natural log logarithm natural In general, a function always has a type.

Most of the built-in functions mentioned above, however, are generic. So in the example above, pi and x could be either of type real or double precision. The compiler would check the types and use the correct version of cos real or double precision. Unfortunately, Fortran is not really a polymorphic language so in general you have to be careful to match the types of your variables and your functions!

Now we turn to the user-written functions. Consider the following problem: A meteorologist has studied the precipitation levels in the Bay Area and has come up with a model r m,t where r is the amount of rain, m is the month, and t is a scalar parameter that depends on the location.

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