Can someone explain how to plot y[n]

I'm very new to MATLAB and I need someone to explain how to plot y[n] over the range -2<n<6. These are the equations I am given:

x[-1]=1
x[0]=2
x[1]=2
x[2]=1
x[3]=4
y[n]=x[n]+y[n-1};
-2<n<6

I have tried but my problem is that I can't use negative indexes in arrays

[Jos (10584)]

• matlab indexing starts at 1
• how is x(n) defined for n > 4
• how is y(n-1) defined?

[Matthew Guiller]

• x(n) for n>4 isnt defined, I just assumed that every value of x(n) other that x(-1) to x(3) is zero.
• y(n-1) isn't defined either, I also just assumed that y(-2) is zero

Answer 1

[dpb]

It's not defined unless you define it and again, Matlab arrays are 1-based (and, unfortunately, inflexible in that).

To handle a case such as this where the axis is negative, you must keep the indices as 1:N but instead of using the value of the timestep or increment as the index, keep a second vector of time values as well as the y vector.

t=-2:6;  % the time steps (or use _n_ if prefer)

Now evaluate y for each value of t, then

plot(t,y)