Determine whether filter is FIR
To determine whether h is an FIR filter, isfir(h) inspects filter h and determines whether the filter, in transfer function form, has a scalar denominator. If it does, it is an FIR filter.
d = fdesign.lowpass; h = design(d); isfir(h) ans = 1
returns 1 for the status of filter h. The filter is an FIR structure with denominator reference coefficient equal to 1.
For multirate filters, isfir works the same way.
d = fdesign.interpolator(5); % Interpolate by 5. h = design(d); % Use the default design method. isfir(h) ans = 1
Use isfir with adaptive filters as well.