الفهرس 
Bif.DOnly 14 pages are availabe for public view
 |  | from | 81 |  |  |
| | | from | 81 | | |
Abstract
Delay di erential equations [1,8,9,17,18,23,33] (DDEs) are employed in mod-
eling many problems in science, engineering, biology and medicine. That is
because the delay term in such equations increases the reliability in modeling
real phenomena and makes the prediction of long term behavior of such mod-
els more accurate. Indeed, (DDEs) represent dynamical system of in nite
dimensions which are opposite to ordinary di erential equations. That is to
say, (DDEs) are a very important topic in dynamical systems. The original
stimulus for the study of (DDEs) mainly lies in the application of control the-
ory and the study of stability and automated management [2,4,16,25{27,30].
Delay equations having multiple time delays, time-dependent delays, and
even continuous distributions of delays all arise in mathematical models of
evolutionary systems [5, 29]. The di erence equation with continuous argu-
ment is one of the principal mathematical instruments of modern nonlinear
dynamics and in the form [13, 19, 31].