soutifu [WP][DOC]: add examples to demonstrate taper application

src/ts/wf/testcases/README.soutifu

@@ -143,4 +143,64 @@ An intermediate value for the exp-parameter will produce a kind of compromise:
 
   make soutifuclean soutifu3x_report.pdp STFPER=0.04 SOUTIFU3EXP=2.5
 
+============================================================================
+Testing special features
+============================================================================
+
+Taper applied to impulse response
+=================================
+All procedures operating in the Fourier domain accept the option "irtap" to
+apply a taper to the impulse response of the source time function corrections
+filter:
+
+  irtap=t1,t2,t3,t4  taper impulse response of correction filter
+
+See the output of "soutifu -phelp fdlsq" (or "onlinehelp -p fdlsq" in the
+source directory of libstfinv) for details. Here are some examples to test
+this feature.
+
+Tests to fail
+-------------
+
+Must fail because taper times must increase monotonically:
+
+  make soutifuclean soutifu1_report.pdp \
+    SOUTIFU1='fdlsq:tshift=0.4:irtap=0.1,0.2,0.1,0.4'
+
+However accepted is:
+
+  make soutifuclean soutifu1_report.pdp \
+    SOUTIFU1='fdlsq:tshift=0.4:irtap=-0.1,-0.1,0.2,0.2'
+
+Tapers longer than the duration of the time series are not accepted:
+
+  make soutifuclean soutifu1_report.pdp \
+    SOUTIFU1='fdlsq:tshift=0.4:irtap=-0.5,-0.1,0.2,2.6'
+
+Tests to demonstrate action
+---------------------------
+
+For 
+
+  make soutifuclean soutifu1_report.pdp NOISEAMP=1.e-5 \
+    SOUTIFU1='fdlsq:tshift=0.4:waterlevel=2.:exp=4.'
+
+the impulse response of the correction filter contains acausal artefacts. They
+and an unwanted coda in the correction filter as well as in the convolved
+synthetics are removed by
+
+  make soutifuclean soutifu1_report.pdp NOISEAMP=1.e-5 \
+    SOUTIFU1='fdlsq:tshift=0.4:waterlevel=2.:exp=4.:irtap=0.,0.05,0.1,0.15'^
+
+Similarly for an intentionally acausal correction filter:
+
+  make soutifuclean soutifu2a_report.pdp NOISEAMP=1.e-6 \
+    SOUTIFU2='fdlsq:tshift=0.4:exp=2.5'
+
+Which can be used to demonstrate the applicability of negative taper
+definition times: 
+
+  make soutifuclean soutifu2a_report.pdp NOISEAMP=1.e-6 \
+    SOUTIFU2='fdlsq:tshift=0.4:exp=2.5:irtap=-0.12,-0.1,-0.02,0.02'
+
 ----- END OF README.soutifu -----