diff --git a/dspl/src/inout.c b/dspl/src/inout.c
index ed41154..a4506f6 100644
--- a/dspl/src/inout.c
+++ b/dspl/src/inout.c
@@ -222,6 +222,34 @@ int DSPL_API writetxt(double* x, double* y, int n, char* fn)
 }
 
 
+/******************************************************************************
+Write a real arrays to the text file "fn"
+*******************************************************************************/
+int DSPL_API writetxt_cmplx(complex_t* x, int n, char* fn)
+{
+  int k;
+  FILE* pFile = NULL;
+  if(!x)
+    return ERROR_PTR;
+  if(n < 1)
+    return ERROR_SIZE;
+  if(!fn)
+    return ERROR_FNAME;
+
+  pFile = fopen(fn, "w+");
+  if(pFile == NULL)
+    return ERROR_FOPEN;
+
+  for(k = 0; k < n; k++)
+    fprintf(pFile, "%+.12E   %+.12E\n", RE(x[k]), IM(x[k]));
+
+
+  fclose(pFile);
+  return RES_OK;
+}
+
+
+
 /******************************************************************************
 Write a int arrays to the text file "fn"
 *******************************************************************************/
diff --git a/examples/src/butter_ap_zp_test.c b/examples/src/butter_ap_zp_test.c
new file mode 100644
index 0000000..af8fa86
--- /dev/null
+++ b/examples/src/butter_ap_zp_test.c
@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "dspl.h"
+
+/* Filter order */
+#define ORD    7
+
+int main(int argc, char* argv[])
+{
+  void* hdspl;  /* DSPL handle        */
+  void* hplot;  /* GNUPLOT handle     */
+  
+  /* Load DSPL functions */
+  hdspl = dspl_load();
+
+  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   */
+
+  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);
+
+  printf("Butterworth filter zeros: %d\n", nz);
+  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]));
+
+  /* Write complex poles to the file */
+  writetxt_cmplx(p, ORD, "dat/butter_ap_zp.txt");
+
+  /* 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 xlabel 'sigma'");
+  gnuplot_cmd(hplot, "set ylabel 'jw'");
+  gnuplot_cmd(hplot, "set size square");
+  gnuplot_cmd(hplot, "set xrange [-1.5:1.5]");
+  gnuplot_cmd(hplot, "set yrange [-1.5:1.5]");
+  gnuplot_cmd(hplot, "plot 'dat/butter_ap_zp.txt'  with points pt 2");
+  gnuplot_close(hplot); 
+
+  /* free dspl handle */
+  dspl_free(hdspl);
+
+  return res;
+}
+
diff --git a/include/dspl.c b/include/dspl.c
index 94672b1..fa2d8ab 100644
--- a/include/dspl.c
+++ b/include/dspl.c
@@ -177,6 +177,7 @@ p_writebin                              writebin                      ;
 p_writetxt                              writetxt                      ;
 p_writetxt_3d                           writetxt_3d                   ;
 p_writetxt_3dline                       writetxt_3dline               ;
+p_writetxt_cmplx                        writetxt_cmplx                ;
 p_writetxt_cmplx_im                     writetxt_cmplx_im             ;
 p_writetxt_cmplx_re                     writetxt_cmplx_re             ;
 p_writetxt_int                          writetxt_int                  ;
@@ -379,6 +380,7 @@ void* dspl_load()
   LOAD_FUNC(writetxt);
   LOAD_FUNC(writetxt_3d);
   LOAD_FUNC(writetxt_3dline);
+  LOAD_FUNC(writetxt_cmplx);
   LOAD_FUNC(writetxt_cmplx_im);
   LOAD_FUNC(writetxt_cmplx_re);
   LOAD_FUNC(writetxt_int);
diff --git a/include/dspl.h b/include/dspl.h
index 1509321..20dd97b 100644
--- a/include/dspl.h
+++ b/include/dspl.h
@@ -960,6 +960,10 @@ DECLARE_FUNC(int,        writetxt_3dline,             double*          x
                                                 COMMA int              n
                                                 COMMA char*            fn);
 /*----------------------------------------------------------------------------*/
+DECLARE_FUNC(int,        writetxt_cmplx,              complex_t*       x
+                                                COMMA int              n
+                                                COMMA char*            fn);
+/*----------------------------------------------------------------------------*/
 DECLARE_FUNC(int,        writetxt_cmplx_im,           double*
                                                 COMMA complex_t*
                                                 COMMA int