;;; PLT Scheme Simulation Collection
;;; Copyright (c) 2005 M. Douglas Williams
;;;
;;; This library is free software; you can redistribute it and/or
;;; modify it under the terms of the GNU Lesser General Public
;;; License as published by the Free Software Foundation; either
;;; version 2.1 of the License, or (at your option) any later version.
;;;
;;; This library is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;; Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this library; if not, write to the Free
;;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
;;; 02111-1307 USA.
;;;
;;; 07/17/05 Cleaned up initialization code.  Added time parameter to
;;;          the constructor.
  
;;; statistics structure
;;;
;;;  #  slot                    description
;;;  -  ----                    -----------
;;;  0  time-dependant?         #t if the statistics are time dependant
;;;  1  time-last-synchronized  time the statistics were last synchronized
;;;  2  minimum                 minimum value
;;;  3  maximum                 maximum value
;;;  4  n                       number of values
;;;  5  sum                     sum of the values
;;;  6  sum-od-squares          sum of the squares of the values
(define-values (struct:statistics
                statistics-constructor
                statistics?
                statistics-field-ref
                set-statistics-field!)
  (make-struct-type 'statistics #f 7 0))

;;; statistics structure, time-dependant? slot
;;; statistics-time-dependant?: statistics -> boolean
;;; set-statistics-time-dependant?!: statistics x boolean -> void
(define statistics-time-dependant?
  (make-struct-field-accessor statistics-field-ref 0 'time-dependant?))
(define set-statistics-time-dependant?!
  (make-struct-field-mutator set-statistics-field! 0 'time-dependant?))

;;; statistics structure, time-last-synchronized slot
;;; statistics-time-last-synchronized: statistics -> real
;;; set-statistics-time-last-synchronized!: statistics x real -> void
(define statistics-time-last-synchronized
  (make-struct-field-accessor statistics-field-ref 1 'time-last-synchronized))
(define set-statistics-time-last-synchronized!
  (make-struct-field-mutator set-statistics-field! 1 'time-last-synchronized))

;;; statistics structure, minimum slot
;;; statistics-minimum: statistics -> real
;;; set-statistics-minimum!: statistics x real -> void
(define statistics-minimum
  (make-struct-field-accessor statistics-field-ref 2 'minimum))
(define set-statistics-minimum!
  (make-struct-field-mutator set-statistics-field! 2 'minimum))

;;; statistics structure, maximum slot
;;; statistics-maximum: statistics -> real
;;; set-statistics-maximum!: statistics x real -> void
(define statistics-maximum
  (make-struct-field-accessor statistics-field-ref 3 'maximum))
(define set-statistics-maximum!
  (make-struct-field-mutator set-statistics-field! 3 'maximum))

;;; statistics structure, n slot
;;; statistics-n: statistics -> real
;;; set-statistics-n!: statistics x real -> void
(define statistics-n
  (make-struct-field-accessor statistics-field-ref 4 'n))
(define set-statistics-n!
  (make-struct-field-mutator set-statistics-field! 4 'n))

;;; statistics structure, sum slot
;;; statistics-sum: statistics -> real
;;; set-statistics-sum!: statistics x real -> void
(define statistics-sum
  (make-struct-field-accessor statistics-field-ref 5 'sum))
(define set-statistics-sum!
  (make-struct-field-mutator set-statistics-field! 5 'sum))

;;; statistics structure, sum-of-squares slot
;;; statistics-sum-of-squares: statistics -> real
;;; set-statistics-sum-of-squares!: statistics x real -> void
(define statistics-sum-of-squares
  (make-struct-field-accessor statistics-field-ref 6 'sum-of-squares))
(define set-statistics-sum-of-squares!
  (make-struct-field-mutator set-statistics-field! 6 'sum-of-squares))

;;; make-statistics: boolean x real -> statistics
(define (make-statistics time-dependant? time)
  (statistics-constructor time-dependant? time +inf.0 -inf.0 0 0.0 0.0))

;;; statistics-accumulate!: statistics x real x real -> void
;;; Accumulate the statistics for the value for the specified time
;;; (actually, duration).
(define (statistics-accumulate! statistics value time)
  (if (< value (statistics-minimum statistics))
      (set-statistics-minimum! statistics value))
  (if (> value (statistics-maximum statistics))
      (set-statistics-maximum! statistics value))
  (let ((weighted-value (* value time))
        (weighted-sum-squared (* value value time)))
    (set-statistics-n!
     statistics (+ (statistics-n statistics) time))
    (set-statistics-sum!
     statistics (+ (statistics-sum statistics) weighted-value))
    (set-statistics-sum-of-squares! 
     statistics (+ (statistics-sum-of-squares statistics)
                   weighted-sum-squared))))

;;; statistics-tally!: statistics x real -> void
;;; Tally the statistics for the value.
(define (statistics-tally! statistics value)
  (statistics-accumulate! statistics value 1))

;;; Pseudo slots

;;; statistics-mean: statistics -> real
(define (statistics-mean statistics)
  (/ (statistics-sum statistics)
     (statistics-n statistics)))

(define (statistics-mean-square statistics)
  (/ (statistics-sum-of-squares statistics)
     (statistics-n statistics)))

(define (statistics-variance statistics)
  (- (statistics-mean-square statistics)
     (* (statistics-mean statistics)
        (statistics-mean statistics))))

(define (statistics-standard-deviation statistics)
  (sqrt (statistics-variance statistics)))