The equations of motion of a 180° domain wall in an infinite uniaxially anisotropic medium which is exposed to an instantaneously applied uniform dc magnetic field H0 have been integrated numerically. Below the critical field Hc =2παM0 (α is the Gilbert loss parameter and M0 the saturation magnetization), where a steady-state solution is known to exist, it is shown that the wall motion tends smoothly to this solution. Above Hc, the magnetization precesses about the field and a periodic component appears in the forward motion of the wall. Analytic solutions for the wall motion have been found based upon approximations suggested by the computed behavior; these reproduce the computer results very accurately.
The development at Bell Laboratorms of PORT, a hbrary of portable Fortran programs for numemcal computation, is discussed. Portab]hty is achmved by careful language specification, together with the key techmque of spemfymg computer classes by means of predefined machine constants The library is built around an automatm error-handling facility and a dynamm storage allocatmn scheme, both of which are implemented portably These, together with the modular structure of the library, lead to slmphfied calhng sequences and ease of use.
DESCRIPTION T h e t h r e e p r o g r a m p a c k a g e s p r e s e n t e d h e r e p r o v i d e a f r a m e w o r k for a p o r t a b l e F o r t r a n s u b r o u t i n e library. T h e y were d e v e l o p e d for t h e Bell L a b o r a t o r i e s l i b r a r y P O R T [1]. T h e p a c k a g e s are: m a c h i n e -d e p e n d e n t c o n s t a n t s , a u t o m a t i c e r r o r handling, a n d d y n a m i c storage a l l o c a t i o n using a stack. T h e r e a r e i n t e r d e p e n d e ncies a m o n g the p a c k a g e s in t h e sense t h a t t h e e r r o r h a n d l i n g is u s e d b y b o t h t h e others, a n d it in t u r n uses m a c h i n e -d e p e n d e n t c o n s t a n t s p r o v i d e d b y t h e first. H o w e v e r , care is t a k e n to a v o i d a n y a c t u a l or a p p a r e n t recursion. T w o n o n -A N S I S t a n d a r d F o r t r a n a s s u m p t i o n s are m a d e in t h e a l g o r i t h m . T h e first is t h a t t h e r e is no r u n t i m e s u b s c r i p t r a n g e checking; t h e s e c o n d is t h a t v a r i a b l e s {local to a s u b p r o g r a m } initialized b y D A T A s t a t e m e n t s , a n d t h e n c h a n g e d w i t h i n t h e s u b p r o g r a m , k e e p t h e i r v a l u e s from one i n v o c a t i o n of t h e s u b p r o g r a m to the next. A p p e n d i x A of [1] discusses n o n s t a n d a r d usage in m o r e detail. REFERENCES 1 Fox, P A., HALL, A.D., AND SCHRYER, N L. The PORT mathematical subroutine library. T h e first p a c k a g e c o n t a i n s t h r e e F o r t r a n f u n c t i o n s u b p r o g r a m s w h i c h can be i n v o k e d to d e t e r m i n e basic m a c h i n e or o p e r a t i n g s y s t e m d e p e n d e n t c o n s t a n t s . V a l u e s are p r o v i d e d in c o m m e n t e d D A T A s t a t e m e n t s for t h e B u r r o u g h s 5700/ Recewed 21 July 1976 and 9 May 1977.General permmslon to make fair use m teaching or research of all or part of this material m granted to individual readers and to nonprofit hbrarms acting for them provided that ACM's copyright notme ]s gwen and that reference is made to the pubhcation, to its date of msue, and to the fact that reprinting prwdeges were granted by permission of the Association for Computing Machinery. To otherwise reprint a figure, table, other substantial excerpt, or the entire work requires specific permission as does republication, or systematm or multiple reproduction.
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