Changes to be committed:

modified:   dspl/dox/en/filter_ap.dox
modified:   dspl/dox/ru/filter_ap.dox
modified:   examples/src/butter_ap_zp_test.c

dspl/dox/en/filter_ap.dox

@@ -52,11 +52,10 @@ Example:
 Result:
 
 \verbatim
-b[ 0] =   1.002   a[ 0] =   1.002
-b[ 1] =   0.000   a[ 1] =   2.618
-b[ 2] =   0.000   a[ 2] =   3.418
-b[ 3] =   0.000   a[ 3] =   2.615
-b[ 4] =   0.000   a[ 4] =   1.000
+b[ 0] =     1.965     a[ 0] =     1.965
+b[ 1] =     0.000     a[ 1] =     3.138
+b[ 2] =     0.000     a[ 2] =     2.505
+b[ 3] =     0.000     a[ 3] =     1.000 
 \endverbatim
 \n
 
@@ -140,6 +139,31 @@ Else \ref ERROR_CODE_GROUP "code error".
 Normalized Butterworth lowpass filter has no finite zeros. 
 So `z` vector will not changed and in pointer `nz` will write 0 value. \n
 
+Example of normalized Butterworth lowpass filter zeros and poles calculation:
+\include butter_ap_zp_test.c
+
+Result:
+
+\verbatim
+Butterworth filter zeros: 0
+Butterworth filter poles: 7
+p[ 0] =    -1.101    +0.000 j
+p[ 1] =    -0.245    +1.074 j
+p[ 2] =    -0.245    -1.074 j
+p[ 3] =    -0.687    +0.861 j
+p[ 4] =    -0.687    -0.861 j
+p[ 5] =    -0.992    +0.478 j
+p[ 6] =    -0.992    -0.478 j  
+\endverbatim
+\n
+
+In `dat` folder will be created `butter_ap_zp.txt` file. \n
+
+In addition, GNUPLOT will build the following graphs 
+from data stored in `dat/butter_ap_zp.txt` file:
+
+\image html butter_ap_zp_test.png
+
 \author Sergey Bakhurin www.dsplib.org
 ***************************************************************************** */
 

dspl/dox/ru/filter_ap.dox

@@ -150,6 +150,32 @@ www.dsplib.org
 Нормированный ФНЧ Баттерворта не имеет нулей, поэтому массив нулей `z` 
 не будет изменен, а по указателю `nz` будет записан 0. \n
 
+
+Пример программы рассчета нулей и полюсов нормированного ФНЧ Баттерворта:
+\include butter_ap_zp_test.c
+
+Результат выполнения программы:
+
+\verbatim
+Butterworth filter zeros: 0
+Butterworth filter poles: 7
+p[ 0] =    -1.101    +0.000 j
+p[ 1] =    -0.245    +1.074 j
+p[ 2] =    -0.245    -1.074 j
+p[ 3] =    -0.687    +0.861 j
+p[ 4] =    -0.687    -0.861 j
+p[ 5] =    -0.992    +0.478 j
+p[ 6] =    -0.992    -0.478 j  
+\endverbatim
+\n
+
+В каталоге `dat` будет создан файл `butter_ap_zp.txt`. \n
+
+Пакет GNUPLOT произведет построение карты полюсов по
+сохранненным в  `dat/butter_ap_zp.txt` данным:
+
+\image html butter_ap_zp_test.png
+
 \author
 Бахурин Сергей
 www.dsplib.org 

examples/src/butter_ap_zp_test.c

@@ -16,19 +16,22 @@ int main(int argc, char* argv[])
 
   complex_t z[ORD+1]; /* H(s) zeros vector */
   complex_t p[ORD+1]; /* H(s) poles vector */
-  double Rp = 1.0; /* Magnitude ripple from 0 to 1 rad/s   */
+  double Rp = 1.0;    /* Magnitude ripple from 0 to 1 rad/s */
 
   int res, k, nz, np;
 
-
   /* Zeros and poles vectors calculation */
   res = butter_ap_zp(ORD, Rp, z, &nz, p, &np);
   if(res != RES_OK)
     printf("error code = 0x%8x\n", res);
 
+  /* print H(s) zeros values */
   printf("Butterworth filter zeros: %d\n", nz);
+  for(k = 0; k < nz; k++)
+    printf("z[%2d] = %9.3f %+9.3f j\n", k, RE(z[k]), IM(p[k]));
+  
+  /* print H(s) poles values */
   printf("Butterworth filter poles: %d\n", np);
-  /* Print H(s) coefficients */
   for(k = 0; k < np; k++)
     printf("p[%2d] = %9.3f %+9.3f j\n", k, RE(p[k]), IM(p[k]));
 
@@ -38,7 +41,8 @@ int main(int argc, char* argv[])
   /* plotting by GNUPLOT */
   gnuplot_create(argc, argv, 440, 360, "img/butter_ap_zp_test.png", &hplot);
   gnuplot_cmd(hplot, "unset key");
-  gnuplot_cmd(hplot, "set grid");
+  gnuplot_cmd(hplot, "set xzeroaxis");
+  gnuplot_cmd(hplot, "set yzeroaxis");
   gnuplot_cmd(hplot, "set xlabel 'sigma'");
   gnuplot_cmd(hplot, "set ylabel 'jw'");
   gnuplot_cmd(hplot, "set size square");