July 17th, 2015, 07:45 AM  #1 
Newbie Joined: Jul 2015 From: Singapore Posts: 2 Thanks: 0  step functions
hi guys, trying to get back to studying, I am doing some basic step functions and all the examples were along the lines of u(t1) now all that is obviously straightforward but they then asked me to plot the graph u(t+1) it is the first I have seen a pos+, do I just move to the left on the x axis sitting alone trying to learn, the simple things drive you nuts. all help appreciated. anyone know any sites to plot functions? thanks stevie 
July 17th, 2015, 09:51 AM  #2 
Math Team Joined: Jan 2015 From: Alabama Posts: 3,159 Thanks: 866 
Yes, u(t 1) is the same as u(x) if x= t 1 so going from "u(x)" to "u(t1)" is the same as shifting the graph one place to the right and going the other way, from u(t 1) to u(x) shifts the graph one place to the left. Then u(t+ 1) is the same as u(x) if x= t+ 1 shifting the graph one place to the left. So going from u(t 1) to u(t+ 1) is shifting the graph two places to the left. (That was for general function, u. Specifically, the step function, u(t 1), is 0 for x< 1 and 1 for x> 1. The step function, u(t+ 1), is 0 for x< 1, 1 for x> 1, so is u(t 1) shifted two places to the left, shifting x= 1 to x= 1.) Last edited by Country Boy; July 17th, 2015 at 10:05 AM. 
July 17th, 2015, 10:11 AM  #3 
Newbie Joined: Jul 2015 From: Singapore Posts: 2 Thanks: 0 
Country Boy, thanks very much for your help, I thought so but couldn't confirm. I could not find one reference to a pos on all my google searches, was starting to get to me. Now to really pester you the very next question was u(t3)u(t2). When graphing it I am slightly confused as with the 3 on the left hand side (of formula) it looks like I am going neg on the 2 (right hand side of formula) before I have gone pos on the 3. Again probably straightforward but when sitting alone the simple things can drive you insane. thanks again for your help Stevie Last edited by stevie1710; July 17th, 2015 at 10:17 AM. 

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