# What would the plot of an two sided digital signal look like?

Please, take a look at section, 1.2.3 (Signal Duration), Page-03, of the book Shaum's Outlines: Digital Signal Processing by by Monson H. Hayes.

According to the definition, I can imagine how a right-sided and a left-sided signal look like. But, I cannot visualize a two-sided signal.

What would an two sided signal look like?

All I need is to see a double-sided signal. As far as I know, a double sided signal is a complex exponential signal. So, that means it should be a plot of a complex exponential function. Am I correct?

• 1) Don't post links to copyrighted material (I've removed the link). 2) It's not clear what you're asking. It's impossible to visualize infinite things. – MBaz Feb 24 '16 at 2:25
• @MBaz, " It's impossible to visualize infinite things" ........ I have added two pictures of two infinite signals. So, your comment is not true. All I need is to see a double-sided signal. As far as I know, a double sided signal is a complex exponential signal. So, that means it should be a plot of a complex exponential function. Am I correct? – user18425 Feb 24 '16 at 2:36
• Not sure what's the problem here. Any signal that extends from $-\infty$ to $\infty$ is a two-sided signal. Classic example: $a^{-|t|}$. No need to use complex signals, even though a complex exponential is indeed also one example of a two-sided signal. – Matt L. Feb 24 '16 at 6:50
• @MBaz I've made an attempt to redact the link, but another mod needs to approve it. I'll ping the other guys later, but feel free to ping me again if you don't see it changed in a reasonable time (the next day or so). – Peter K. Feb 24 '16 at 12:43

A function of $x$ is right-sided if and only if there is some $x_0$ such that the value of the function is zero for all $x < x_0$, and left-sided if and only if there is some $x_0$ such that the value of the function is zero for all $x > x_0$.
Likewise for signals with time represented by $x$. A double-sided signal has neither restriction. For example a Gaussian function and $\sin(x)$ (both pictured below) are double-sided. $f(x) = \frac{e^{-\frac{x^2}{2}}}{\sqrt{2 \pi }}$
• @anonymous well, in my plots, if you imagine a marker on those functions at each integer $x$ then those markers are a "plot" of a discrete signal. – Olli Niemitalo Feb 24 '16 at 14:38