Cumulative standard deviation: Difference between revisions

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 =={{header|Forth}}==
-{{incorrect|Forth|It does not return the ''running'' standard deviation of the series.}}
 <lang forth>: f+! ( x addr -- ) dup f@ f+ f! ;
@@ Line 1,158: / Line 1,157: @@
 : st-sum   ( stats -- sum )       float+   f@ ;
 : st-sumsq ( stats -- sum*sum ) 2 floats + f@ ;
-: st-add ( fnum stats -- )
-e dup f+!  float+
-  fdup dup f+!  float+
-  fdup f*  f+! ;
 : st-mean ( stats -- mean )
@@ Line 1,173: / Line 1,167: @@
 : st-stddev ( stats -- stddev )
-  st-variance fsqrt ;</lang>
+  st-variance fsqrt ;
+: st-add ( fnum stats -- )
+  dup
+e dup f+!  float+
+  fdup dup f+!  float+
+  fdup f*  f+!
+  std-stddev ;</lang>
 This variation is more numerically stable when there are large numbers of samples or large sample ranges.
 <lang forth>: st-count ( stats -- n )                f@ ;
@@ Line 1,183: / Line 1,185: @@
 : st-add ( x stats -- )
+  dup
 e dup f+!			\ update count
   fdup dup st-mean f- fswap
@@ Line 1,190: / Line 1,193: @@
   float+ dup f+!		\ update mean
   ( delta x )
-  dup f@ f-  f*  float+ f+! ;	\ update nvar</lang>
+  dup f@ f-  f*  float+ f+!	\ update nvar
+  st-stddev ;</lang>
+Usage example:
 <lang forth>create stats 0e f, 0e f, 0e f,
-e stats st-add
+e stats st-add f. \ 0.
-e stats st-add
+e stats st-add f. \ 1.
-e stats st-add
+e stats st-add f. \ 0.942809041582063
-e stats st-add
+e stats st-add f. \ 0.866025403784439
-e stats st-add
+e stats st-add f. \ 0.979795897113271
-e stats st-add
+e stats st-add f. \ 1.
-e stats st-add
+e stats st-add f. \ 1.39970842444753
-e stats st-add
+e stats st-add f. \ 2.
+</lang>
-stats st-stddev f.   \ 2.</lang>
 =={{header|Fortran}}==