| Signal Processing Toolbox | |
Find initial conditions for a transposed direct form II filter implementation.
Syntax
z=filtic(b,a,y,x) z=filtic(b,a,y)
Description
z finds the initial conditions, = filtic(b,a,y,x)
z, for the delays in the transposed direct form II filter implementation given past outputs y and inputs x. The vectors b and a represent the numerator and denominator coefficients, respectively, of the filter's transfer function.
The vectors x and y contain the most recent input or output first, and oldest input or output last.
where nb is length(b)-1 (the numerator order) and na is length(a)-1 (the denominator order). If length(x) is less than nb, filtic pads it with zeros to length nb; if length(y) is less than na, filtic pads it with zeros to length na. Elements of x beyond x(nb-1) and elements of y beyond y(na-1) are unnecessary so filtic ignores them.
Output z is a column vector of length equal to the larger of nb and na. z describes the state of the delays given past inputs x and past outputs y.
z assumes that the input = filtic(b,a,y)
x is 0 in the past.
The transposed direct form II structure is
where n-1 is the filter order.
filtic works for both real and complex inputs.
Algorithm
filtic performs a reverse difference equation to obtain the delay states z.
Diagnostics
If any of the input arguments y, x, b, or a is not a vector (that is, if any argument is a scalar or array), filtic gives the following error message.
Requires vector inputs.
See Also
|
Filter data with a recursive (IIR) or nonrecursive (FIR) filter. |
|
Zero-phase digital filtering. |
References
[1] Oppenheim, A.V., and R.W. Schafer, Discrete-Time Signal Processing, Prentice-Hall, 1989, pp. 296, 301-302.
| | filtfilt | fir1 | |