feat: Add S_n and S_n0 statistics

Closes #6

Author: fraya

doc/source/gsl-ffi-statistics.rst

@@ -507,3 +507,25 @@ Robust Scale Estimates
    :parameter work: An instance of `<c-double*>`.
    :value mad: An instance of `<c-double>`.
 
+:math:`S_n` Statistic
+=====================
+
+.. function:: gsl-stats-sn0-from-sorted-data
+
+   :signature: gsl-stats-sn0-from-sorted-data (sorted-data stride n work) => (sn0)
+
+   :parameter sorted-data: An instance of `<c-double*>`.
+   :parameter stride: An instance of `<c-size-t>`.
+   :parameter n: An instance of `<c-size-t>`.
+   :parameter work: An instance of `<c-double*>`.
+   :value sn0: An instance of `<c-double>`.
+
+.. function:: gsl-stats-sn-from-sorted-data
+
+   :signature: gsl-stats-sn-from-sorted-data (sorted-data stride n work) => (sn)
+
+   :parameter sorted-data: An instance of `<c-double*>`.
+   :parameter stride: An instance of `<c-size-t>`.
+   :parameter n: An instance of `<c-size-t>`.
+   :parameter work: An instance of `<c-double*>`.
+   :value sn: An instance of `<c-double>`.

doc/source/gsl-statistics.rst

@@ -300,4 +300,21 @@ Robust Scale Estimates
 
    :parameter data: An instance of :class:`<gsl-vector>`.
    :parameter #key stride: An instance of :drm:`<integer>`.
-   :value mad0: An instance of :drm:`<double-float>`.
+   :value mad0: An instance of :drm:`<double-float>`.
+
+:math:`S_n` Statistic
+=====================
+
+.. function:: sn0
+
+   :signature: sn0 (sorted-data) => (sn0)
+
+   :parameter data: An instance of :class:`<gsl-vector>`.
+   :value sn0: An instance of :drm:`<double-float>`.
+
+.. function:: sn
+
+   :signature: sn (sorted-data) => (sn)
+
+   :parameter data: An instance of :class:`<gsl-vector>`.
+   :value sn: An instance of :drm:`<double-float>`.

src/lib/ffi/module-statistics.dylan

@@ -7,7 +7,7 @@ Reference: https://www.gnu.org/software/gsl/doc/html/statistics.html
 
 define module gsl-ffi-statistics
 
-  // Mean, Standard Deviation and Variance (file:./mean-std-variance.dylan)
+  // Mean, Standard Deviation and Variance
 
   create
     gsl-stats-mean,
@@ -20,46 +20,46 @@ define module gsl-ffi-statistics
     gsl-stats-variance-with-fixed-mean,
     gsl-stats-sd-with-fixed-mean;
 
-  // Absolute deviation (file:./absolute-deviation.dylan)
+  // Absolute deviation
 
   create
     gsl-stats-absdev,
     gsl-stats-absdev-m;
 
-  // Higher moments (file:./higher-moments.dylan)
+  // Higher moments
 
   create
     gsl-stats-skew,
     gsl-stats-skew-m-sd,
     gsl-stats-kurtosis,
     gsl-stats-kurtosis-m-sd;
 
-  // Autocorrelation (file:./autocorrelation.dylan)
+  // Autocorrelation
 
   create
     gsl-stats-lag1-autocorrelation,
     gsl-stats-lag1-autocorrelation-m;
 
-  // Covariance (file:./covariance.dylan)
+  // Covariance
 
   create
     gsl-stats-covariance,
     gsl-stats-covariance-m;
 
-  // Maximum and Minimum (file:./maximum-minimum.dylan)
+  // Maximum and Minimum
 
   create
     gsl-stats-max,
     gsl-stats-min,
     gsl-stats-minmax;
 
-  // Correlation (file:./correlation.dylan)
+  // Correlation
 
   create
     gsl-stats-correlation,
     gsl-stats-spearman;
 
-  // Weighted samples (file:./weighted-samples.dylan)
+  // Weighted samples
 
   create
     gsl-stats-wmean,
@@ -77,29 +77,35 @@ define module gsl-ffi-statistics
     gsl-stats-wkurtosis,
     gsl-stats-wkurtosis-m-sd;
 
-  // Median and percentiles (file:./median-percentiles.dylan)
+  // Median and percentiles
 
   create
     gsl-stats-median-from-sorted-data,
     gsl-stats-median;
 
-  // Order statistics (file:./order-statistic.dylan)
+  // Order statistics
 
   create
     gsl-stats-select;
 
-  // Robust location estimates (file:./robust-location-estimates.dylan)
+  // Robust location estimates
 
   create
     gsl-stats-trmean-from-sorted-data,
     gsl-stats-gastwirth-from-sorted-data;
 
-  // Robust scale estimates (file:./robust-scale-estimates.dylan)
+  // Robust scale estimates
 
   create
     gsl-stats-mad,
     gsl-stats-mad0;
 
+  // S_n statistic
+
+  create
+    gsl-stats-sn0-from-sorted-data,
+    gsl-stats-sn-from-sorted-data;
+
 end module;
 
 define module gsl-ffi-statistics-impl

src/lib/ffi/statistics.dylan

@@ -624,5 +624,33 @@ define c-function gsl-stats-mad
    c-name: "gsl_stats_mad";
 end;
 
-// TODO: S_n Statistics
+//////////////////////////////////////////////////////////////////////////////
+//
+// S_n Statistic
+//
+// https://www.gnu.org/software/gsl/doc/html/statistics.html#s-n-statistic
+//
+// https://www.gnu.org/software/gsl/doc/html/statistics.html#c.gsl_stats_Sn0_from_sorted_data
+// https://www.gnu.org/software/gsl/doc/html/statistics.html#c.gsl_stats_Sn_from_sorted_data
+//
+//////////////////////////////////////////////////////////////////////////////
+
+define c-function gsl-stats-sn0-from-sorted-data
+   parameter sorted-data :: <c-double*>;
+   parameter stride :: <c-size-t>;
+   parameter n :: <c-size-t>;
+   parameter work :: <c-double*>;
+   result sn0 :: <c-double>;
+   c-name: "gsl_stats_Sn0_from_sorted_data";
+end;
+
+define c-function gsl-stats-sn-from-sorted-data
+   parameter sorted-data :: <c-double*>;
+   parameter stride :: <c-size-t>;
+   parameter n :: <c-size-t>;
+   parameter work :: <c-double*>;
+   result sn :: <c-double>;
+   c-name: "gsl_stats_Sn_from_sorted_data";
+end;
+
 // TODO: Q_n Statistics

src/lib/gsl/module-statistics.dylan

@@ -34,7 +34,8 @@ define module gsl-statistics
     trimmed-mean,
     gastwirth-estimator,
     mad,
-    mad0;
+    mad0,
+    sn0;
 
 end module;
 

src/lib/gsl/statistics.dylan

@@ -550,5 +550,35 @@ define function mad
   end
 end;
 
-// TODO: S_n Statistics
+//////////////////////////////////////////////////////////////////////////////
+//
+// S_n Statistic
+//
+// https://www.gnu.org/software/gsl/doc/html/statistics.html#s-n-statistic
+//
+// https://www.gnu.org/software/gsl/doc/html/statistics.html#c.gsl_stats_Sn0_from_sorted_data
+// https://www.gnu.org/software/gsl/doc/html/statistics.html#c.gsl_stats_Sn_from_sorted_data
+//
+//////////////////////////////////////////////////////////////////////////////
+
+define function sn0
+    (sorted-data :: <gsl-vector>)
+ => (sn0 :: <double-float>)
+ let n = sorted-data.size;
+ with-stack-structure (work :: <c-double*>, element-count: n)
+   gsl-stats-sn0-from-sorted-data
+     (sorted-data.%gsl-vector-data, sorted-data.gsl-vector-stride, n, work)
+ end
+end;
+
+define function sn
+    (sorted-data :: <gsl-vector>)
+ => (sn :: <double-float>)
+ let n = sorted-data.size;
+ with-stack-structure (work :: <c-double*>, element-count: n)
+   gsl-stats-sn-from-sorted-data
+     (sorted-data.%gsl-vector-data, sorted-data.gsl-vector-stride, n, work)
+ end
+end;
+
 // TODO: Q_n Statistics