Separate HTML for Basic Foil 4 Why is Fortran90 Easier than Fortran77

Basic HTML version of Foils prepared 17 Sept 1996

Foil 4 Why is Fortran90 Easier than Fortran77

From New CPS615HPF and Fortran90 Discussion Sept 17 96 Basic Simulation Track for Computational Science CPS615 -- Fall Semester 96. by Geoffrey C. Fox, Tom Haupt

Do 1 I=1,N

1 A(I)=B(I) is obviously parallel

Fortran90 Array Notation

A=B expresses this parallelism naturally in way compiler can easily detect in a deterministic way
Do 1 I=1,N
J=I
K=I

1 A(J)=B(K) is not so obviously parallel

Needs a difficult to define (in general case) algorithm (especially if IF statements, i.e. conditionals, defining I,J) to decide on existence and implementation of parallelism

Use of Fortran77 has "thrown away" natural parallelism at language level even though "run-time" restores as creates explicit values for variables such as J and K which are only known by analysis at compile time.