libpsdxx [WP][FEATURE]: implement function lin_frequency

src/libs/libpsdxx/function_lin_frequency.cc

@@ -34,9 +34,25 @@
   "PSDXX_FUNCTION_LIN_FREQUENCY_CC   V1.0"
 
 #include <psdxx/psd.h>
+#include <psdxx/error.h>
 
 namespace psd {
 
+   TDseries lin_frequency(const double& df, 
+                          unsigned int& nsamples)
+   {
+     PSDXX_assert(nsamples>0,
+                  "at least one sample must be present");
+     TDseries retval(0,nsamples-1);
+     for (int i=retval.f(); i<=retval.l(); ++i)
+     {
+       retval(i)=df*i;
+     }
+     return(retval);
+   } // TDseries lin_frequency(const double& df, 
+     //                        unsigned int& nsamples)
+
+
 } // namespace psd
 
 /* ----- END OF function_lin_frequency.cc ----- */