[Commit-gnuradio] [gnuradio] 01/01: Made iir_filter documentation more beginner-friendly, removed cruft.

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jcorgan pushed a commit to branch maint
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commit c02765b31090887ba32b3b468b75174a3a18057b
Author: Laur Joost <address@hidden>
Date:   Mon Apr 18 13:57:34 2016 +0300

    Made iir_filter documentation more beginner-friendly, removed cruft.
    
    Documentation has a line claiming that fftaps and fbtaps have to be the 
same length.
    This is, it seems, no longer true.
    
    Also added symbol definitions for the math, disambiguated the difference 
equation
    wrt. 'oldstyle'.
---
 gr-filter/include/gnuradio/filter/iir_filter.h | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/gr-filter/include/gnuradio/filter/iir_filter.h 
b/gr-filter/include/gnuradio/filter/iir_filter.h
index 0f21472..0f2b1e5 100644
--- a/gr-filter/include/gnuradio/filter/iir_filter.h
+++ b/gr-filter/include/gnuradio/filter/iir_filter.h
@@ -88,8 +88,6 @@ namespace gr {
         * This filter uses the Direct Form I implementation, where
         * \p fftaps contains the feed-forward taps, and \p fbtaps the feedback 
ones.
         *
-        * \p fftaps and \p fbtaps must have equal numbers of taps
-        *
         * \p oldstyle: The old style of the IIR filter uses feedback
         * taps that are negative of what most definitions use (scipy
         * and Matlab among them). This parameter keeps using the old
@@ -97,17 +95,27 @@ namespace gr {
         * generated from scipy, Matlab, or gr_filter_design, use the
         * new style by setting this to FALSE.
         *
-        * The input and output satisfy a difference equation of the form
+        * When \p oldstyle is set FALSE, the input and output satisfy a
+        * difference equation of the form
 
         \f[
-        y[n] \pm \sum_{k=1}^{M} a_k y[n-k] = \sum_{k=0}^{N} b_k x[n-k]
+        y[n] + \sum_{k=1}^{M} a_k y[n-k] = \sum_{k=0}^{N} b_k x[n-k]
         \f]
 
         * with the corresponding rational system function
 
         \f[
-        H(z) = \frac{\sum_{k=0}^{N} b_k z^{-k}}{1 \pm \sum_{k=1}^{M} a_k 
z^{-k}}
+        H(z) = \frac{\sum_{k=0}^{N} b_k z^{-k}}{1 + \sum_{k=1}^{M} a_k z^{-k}}
         \f]
+        * where:
+        * \f$x\f$ - input signal,
+        * \f$y\f$ - output signal,
+        * \f$a_k\f$ - k-th feedback tap,
+        * \f$b_k\f$ - k-th feed-forward tap,
+        * \f$M\f$ - \p len(fbtaps)-1,
+        * \f$N\f$ - \p len(fftaps)-1.
+
+        *  \f$a_0\f$, that is \p fbtaps[0], is ignored.
         */
        iir_filter(const std::vector<tap_type>& fftaps,
                   const std::vector<tap_type>& fbtaps,