Signals and systems - zero state response

[LM741]

hey something is really confusing me...

we are given this impulse response

h[k] = 2d[k] +((0.8)^k).u[k] + (2(-0.4)^k).u[k]

where d is delta...
anyway the question then asks:

using the convolution, determine the ZERO STATE RESPONSE for an input signal x[k] = 2u[k+2] - 2u[k-4].

Now i kown how to solve that using the convoltion sum (as required):

[tex] y[n] = x[n] * h[n] = \sum_{k=-\infty}^{\infty}h[k] x[n-k][/tex]

my only problem is that this evaluates the total reponse, y[k]!
where our total reponse is equal to the zero state response and the zero input response...
but we just want zero state response - my peers and a tutor say that the convoltution sum is just the zero state response!
is this true...?
they also told me that the zero state response is not necessarily the forced response - (but in textbooks and other sources they always refer to these as the same thing)
thanks...

 

[anorlunda]

In electrical circuit theory, the zero state response (ZSR), also known as the forced response is the behavior or response of a circuit with initial state of zero. The ZSR results only from the external inputs or driving functions of the circuit and not from the initial state. The ZSR is also called the forced or driven response of the circuit.

The total response of the circuit is the superposition of the ZSR and the ZIR, or Zero Input Response. The ZIR results only from the initial state of the circuit and not from any external drive. The ZIR is also called the natural response, and the resonant frequencies of the ZIR are called the natural frequencies. Given a description of a system in the s-domain, the zero-state response can be described as Y(s)=Init(s)/a(s) where a(s) and Init(s) are system-specific.