Step function

Discussion in 'Homework Help' started by Anthony Quah, Mar 30, 2008.

  1. Anthony Quah

    Thread Starter Active Member

    Dec 1, 2007
    i need some help with this equation of step function,

    x(n) = 2u(n-1)

    i dont know how the equation with "2u" will look like...cause normal..i see in the book is only "u" but this equation got two in it..i am little is the amplitude of the signal..i have attach a graph hope someone can let me know if i am in the right path. Thank
  2. Mark44

    Well-Known Member

    Nov 26, 2007
    The "u" is the name of the function, unit step function. The quantity in parentheses, n - 1, indicates that the graph of the step function is translated to the right by one unit. The multiplier 2 indicates that the graph is scaled by a factor of 2 away from the horizontal axis.

    I'm going to rewrite your equation, assuming it's defined for real numbers, and using y for the vertical axis and t for the horizontal:
    y(t) = 2*u(t - 1)

    Then y(t) = 0 if t < 1, and
    y(t) = 2 if t >= 1

    In your version, you used n as the independent variable. Often n is used for a function that is defined only on integer values. If that really is how your function is defined, instead of two horizontal lines, what you get is two sets of points that lie on the two horizontal lines.

    Is that enough of a start?