A Brief Introduction to Fortran 77 - Polaris

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VariablesVariables in Fortran 77 start with a letter, contain only lettersand digits, and are no more than six characters long. In Fortran90 up to 31 characters are allowed and the underscore _ canform part of the variable name.The type of variables is specified either explicitly in a typedeclaration statement or is implicit. Examples of typedeclaration statements:real a,b,c(10,10)integer i,j,k(100)double precision ...complex ...logical q, p rcharacter s,t * 5,u(20,20)character * 10 v, w, yThe * num in the character statement specifies the length ofthe variable in number of characters. It applies to the whole listif it appears after the character keyword, or to the variable ifit appears after a variable name.© 1998 David A. Padua10 of 118
A scalar variable does not have to be declared in Fortran. Thefirst letter of an undeclared variable indicates its type. Variablesstarting with letter I thorough N (INteger) are of type integervariables. All other undeclared variables are of type real.This default option can be changed with the IMPLICITstatement.An array declarator is a variable name followed by aspecification of the dimensions. The dimension specificationhas the form ( d 1 , d 2 ,...) where d i s represent thesize of each dimension. In the main program the dimensionsare specified using integer constants. They could be a singleinteger, say n, meaning that the possible subscripts are fromone to n. Also, they could be a pair of integers, say m:n,meaning that the values of the subscripts for that dimensionhave to be between n and m.© 1998 David A. Padua11 of 118
Page 1 and 2: A Brief Introduction to Fortran 771
Page 3 and 4: InterpretersAn interpreter is a pro
Page 5 and 6: Source formTraditionally, Fortran s
Page 7 and 8: Lower case letters are considered e
Page 9: The form of a character constant is
Page 13 and 14: ExpressionsExpressions in Fortran c
Page 15 and 16: The logical operators are:.NOT. Log
Page 17 and 18: 3. DO statement. Iterative statemen
Page 19 and 20: Program UnitsA Fortran program alwa
Page 21 and 22: Notice that the variable y in the l
Page 23 and 24: Each read starts on the next record
Page 25 and 26: function rtflsp(func,x1,x2,xacc)par
Page 27 and 28: A Brief Introduction to Fortran 90
Page 29 and 30: IMPLICIT none29 of 118
Page 31 and 32: Array Shapes and SizesThe shape of
Page 33 and 34: Fortran 90 Intrinsic Proceduresaint
Page 35 and 36: Finer control on when an array is c
Page 37 and 38: Procedure InterfacesWhen a procedur
Page 39 and 40: Expressions in Fortran 90 may conta
Page 41 and 42: In the following compound statement
Page 43 and 44: 6.1 IntroductionOpenMP is a collect
Page 45 and 46: All variables are assumed to be sha
Page 47 and 48: Notice that the first statement can
Page 49 and 50: 6.4 The PSINGLE directiveFinally, s
Page 51 and 52: A better example of psingle:c$ompc$
Page 53 and 54: The syntax of the pdo directive is
Page 55 and 56: 6.6 The PARALLEL DO directiveAn alt
Page 57 and 58: And the routine pdo_2 can be rewrit
Page 59 and 60: 6.7 The PSECTIONS directiveAn alter
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end© 1998 David A. Padua61 of 118
Page 63 and 64:
Chapter 7. Parallel Loops in OpenMP
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Chapter 6. OpenMP65 of 118
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Another example of a race is:c$omp
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Another example is:c$ompparallel do
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7.2 Race-free parallel loopsNext, w
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7.3 PrivatizationSometimes the tran
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Sometimes it is necessary to privat
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One way to solve this problem is to
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Variables in lastprivate are privat
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print *,a(1),a(2)endprints1.000000
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To account for this, a and b should
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Most induction variables are quite
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Here, again, only the induction var
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The way to remove the races produce
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We can now proceed as above to obta
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However, there is a way to improve
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Notice that now no races exist beca
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7.6 Execution time of a parallel do
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following time lines:abcdeDabcdeDDa
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7.6 Critical Regions and Reductions
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Here, we use the critical directive
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The assumption is that it does not
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© 1998 David A. Padua108 of 118
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A Brief Introduction to Fortran 77 - Polaris

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