filter_disc_var :
A variable discrete-time filter for xreal-typed signals.

The filter_disc_var primitive models a discrete-time filter with an xreal-typed input, of which transfer function can be time-varying, controlled by real-typed inputs.

The primitive samples the input in at the rising edge of the trigger signal trig and processes the sampled signal with the following z-domain transfer function controlled by the inputs num and den to produce the output out:

             a0 + a1*z^(-1) + a2*z^(-2) + ... + aN*z^(-N)
    H(z) = ------------------------------------------------
             b0 + b1*z^(-1) + b2*z^(-2) + ... + bM*z^(-M)

where the numerator coefficients a0, a1, …, aN are set by the real-typed array input num (i.e., num[0:N] = ‘{a0, a1, …, aN}) and the denominator coefficients b0, b1, …, bM are set by the real-typed array input den (i.e., den[0:M] = ‘{b0, b1, …, bM}). The value of the coefficient b0 (i.e. den[0]) must not be zero at all times. The parameters order_num and order_den specify the order of the numerator (N) and the order of the denominator (M) of the transfer function, respectively.

If the order of the denominator order_den is 0 (i.e., M=0), the primitive models a discrete-time filter with a finite impulse response (FIR). Otherwise, the primitive models a discrete-time filter with an infinite impulse response. The parameter init_value specifies the initial output value of the filter.

Input/Output Terminals

Name	I/O	Type	Description
out	output	xreal	output signal
in	input	xreal	input signal
trig	input	xbit	trigger signal
num	input	real	numerator coefficients
den	input	real	denominator coefficients

Parameters

Name	Type	Default	Unit	Description
order_num	integer	0	None	order of numerator
order_den	integer	0	None	order of denominator
init_value	real	`NaN	None	initial output value