Last modified on Mon Aug 26 22:55:30 1991 by kalsow modified on Thu Nov 2 18:11:42 1989 by muller

modified on Thu Aug 4 08:14:28 1988 by stolfi modified on Fri Jun 10 14:23:17 PDT 1988 by glassman

INTERFACE Stat;

IMPORT Wr, Thread;

TYPE
  T = RECORD (* A statistics accumulator *)
        num      : LONGREAL;
        mean     : LONGREAL;
        variance : LONGREAL;
        maximum  : REAL;
        minimum  : REAL;
      END;

  (* Typical usage:
  |    VAR st: Stat.T;
  |    BEGIN
  |      Stat.Init(st);
  |      LOOP
  |        weight := ...
  |        Stat.Accum(st, weight);
  |        ...
  |      END;
  |      Wr.PrintF(stderr, "Weight statistics: ");
  |      Stat.Print(stderr, st);
  |      Wr.PrintF(stderr, "\n");
  |    END;
  The mean is arithmetic mean.  The variance is the sum of of
  (x - mean)**2, divided by num (NOT num-1).  Thus, the standard
  deviation is sqrt(variance*num/(num-1)).  *)

PROCEDURE Init (VAR s: T);

Resets the statistics accumulator s

PROCEDURE Accum (VAR s: T; x: REAL);

Accumulates another observation x into the statistics accumulator s

PROCEDURE Combine (READONLY r, s: T): T;

Combines statistics of two disjoint samples into a single sample

PROCEDURE Num (READONLY s: T): REAL;

The number of observations in s. Same as FLOAT(s.num).

PROCEDURE Max (READONLY s: T): REAL;

The maximum observed value. Same as s.maximum.

PROCEDURE Min (READONLY s: T): REAL;

The minimum observed value. Same as s.minimum.

PROCEDURE Mean (READONLY s: T): REAL;

The arithmetic mean. Same as FLOAT(s.mean).

PROCEDURE Var (READONLY s: T): REAL;

The variance, i.e. sum((x[i]-mean)^2)/num. Same as FLOAT(s.variance).

PROCEDURE SDev (READONLY s: T): REAL;

The standard deviation, sqrt(sum((x[i]-mean)^2)/(num-1)).

PROCEDURE RMS (READONLY s: T): REAL;

The root mean square value, sqrt(sum(x[i]^2)/num)

PROCEDURE Print (wr: Wr.T;  READONLY s: T) RAISES {Wr.Failure, Thread.Alerted};

Prints the text string

          "num: %d  min: %g  max: %g  mean: %g  dev: %g"
   

on the given writer. If num=0, all other entries are omitted. The dev entry is the standard deviation, and is omitted if num<=1.

END Stat.