math: Improve comments.

[pspp] / src / math / np.c

diff --git a/src/math/np.c b/src/math/np.c
index ccaa51e22d24a0e96a91996f7f597df547d3c6ce..220865ba3cbec59602ec9afccce2a6c193de813b 100644 (file)
--- a/src/math/np.c
+++ b/src/math/np.c
@@ -47,7 +47,7 @@ acc (struct statistic *s, const struct ccase *cx UNUSED,
   struct np *np = UP_CAST (s, struct np, parent.parent);
   double rank = np->prev_cc + (c + 1) / 2.0;
 
-  double ns = gsl_cdf_ugaussian_Pinv (rank / ( np->n + 1 ));
+  double ns = gsl_cdf_ugaussian_Pinv (rank / (np->n + 1));
 
   double z = (y - np->mean) / np->stddev;
 
@@ -63,19 +63,29 @@ acc (struct statistic *s, const struct ccase *cx UNUSED,
   minimize (&np->y_min, y);
 
   cp = case_create (casewriter_get_proto (np->writer));
-  case_data_rw_idx (cp, NP_IDX_Y)->f = y;
-  case_data_rw_idx (cp, NP_IDX_NS)->f = ns;
-  case_data_rw_idx (cp, NP_IDX_DNS)->f = dns;
+  *case_num_rw_idx (cp, NP_IDX_Y) = y;
+  *case_num_rw_idx (cp, NP_IDX_NS) = ns;
+  *case_num_rw_idx (cp, NP_IDX_DNS) = dns;
   casewriter_write (np->writer, cp);
 
   np->prev_cc = cc;
 }
 
+/* Creates and returns a data structure whose accumulated results can be used
+   to produce a normal probability plot.  The caller must supply the weighted
+   sample size N and the mean MEAN and variance VAR of the distribution, then
+   feed in the data with order_stats_accumulate() or
+   order_stats_accumulate_idx().
+
+   There is no function to produce the results, which appear in "struct np" for
+   passing directly to np_plot_create() or dnp_plot_create().
+
+   The caller must eventually destroy the returned structure, with
+   statistic_destroy(). */
 struct np *
-np_create (const struct moments1 *m)
+np_create (double n, double mean, double var)
 {
-  double variance;
-  struct np *np = xzalloc (sizeof (*np));
+  struct np *np = XZALLOC (struct np);
   struct order_stats *os = &np->parent;
   struct statistic *stat = &os->parent;
   struct caseproto *proto;
@@ -83,9 +93,10 @@ np_create (const struct moments1 *m)
 
   np->prev_cc = 0;
 
-  moments1_calculate (m, &np->n, &np->mean, &variance, NULL, NULL);
+  np->n = n;
+  np->mean = mean;
 
-  np->stddev = sqrt (variance);
+  np->stddev = sqrt (var);
 
   np->y_min = np->ns_min = np->dns_min = DBL_MAX;
   np->y_max = np->ns_max = np->dns_max = -DBL_MAX;