Textbook definition of causal

On Oct 14, 1:41&#4294967295;am, "italrosso" <martin.elli...@economics.ox.ac.uk>
wrote:
> Please humour an economist coming here in peace!
>
> I am trying to track down the classic textbook definition of a causal
> system. I know it is a system which only depends on current and previous
> input values but it would be nice to know what is THE reference for this.
>
> I was browsing through past messages on this board and it seems that
> people may be able to help.
>
> Thanks very much in advance.

I would say that for a system with input u(t) and output y(t) that if u
(t)=1 for t>0 then

y(-t)=0 for t>0


Hardy

italrosso wrote:
> Please humour an economist coming here in peace!
> 
> I am trying to track down the classic textbook definition of a causal
> system. I know it is a system which only depends on current and previous
> input values but it would be nice to know what is THE reference for this.
> 
> I was browsing through past messages on this board and it seems that
> people may be able to help.
> 
> Thanks very much in advance.
> 
> 

Seems to me that there's been a whole lot of "comment" with very little 
illumination.


"THE" reference?  That's likely elusive.
"THE" textbook definition is THE definition in THE textbook and varies 
from textbook to textbook.
Why do you care about finding THE classic textbook definition?  It 
likely doesn't exist.

I'm not being snide, just trying to get some clarification.....

Now, if you're interested in a definition then you've read quite  few by 
now.  My bias would be to go to differential equations and consider how 
they generally work - including the definition of the time frame and 
where t=0 is.  But that seems just a reiteration of your original post 
so I focus here on your original *question*.

Fred