libpsdxx [WP]: add function prototype lin_frequency

src/libs/libpsdxx/psd.h

@@ -209,6 +209,18 @@ namespace psd {
 
   /* ====================================================================== */
 
+   /*! return a linear frequency scale
+    *
+    * \param df sampling interval in Hz of uniformly samples spectral values
+    * \param nsamples number of samples of spectral data
+    * \return series of frequency values in Hz with linear spacing with \p df
+    *         interval beginning with 0 Hz
+    *
+    * This function is a corresponding function to log_frequency().
+    */
+   TDseries lin_frequency(const double& df, 
+                          unsigned int& nsamples);
+
    /*! return a logarithmic frequency scale
     *
     * \param df sampling interval in Hz of uniformly samples spectral values
@@ -222,9 +234,9 @@ namespace psd {
     * logarithmic spacing. The return value can be used as input parameter to
     * the actual sampling functions.
     */
-  TDseries log_frequency(const double& df, 
-                         unsigned int& nsamples,
-                         unsigned int& n_per_decade);
+   TDseries log_frequency(const double& df, 
+                          unsigned int& nsamples,
+                          unsigned int& n_per_decade);
 
    /*! sample values on a logarithmic frequency axis
     */