隨機函數總是返回相同的結果，儘管不同的種子

Question

我試圖創建一個隨機數字發生器（從中隨機數字稍後將被轉換成[A-Z]字符）。我有隨機發生器的主要部分工作，但我不斷收到相同的隨機結果0.6734141422。

我正面臨着另一個問題：我的程序編譯速度過快一半。由於我以毫秒爲單位使用當前日期，所以讓我的程序快速編譯將意味着RANDOM函數會使用相同的種子。我一直在考慮簡單地添加一個計數器，它會將每個種子的計數器分配到RANDOM之前。這是否足夠，還是有更多優雅的解決方案？

有人可以向我解釋爲什麼我總是收到相同的隨機結果，即使應用不同的種子值？每次執行程序時我都會得到這個結果。

我正在使用PerCobol編譯器，就像我讀過的那樣，它與OpenCobol一致。

綜上所述：

• 我應該如何克服等於種子隊？

• 爲什麼我用不同的種子接收相同的隨機結果？

  000100 IDENTIFICATION DIVISION. 
  000200 PROGRAM-ID. RandomTest. 
  
  ENVIRONMENT DIVISION. 
  
      DATA DIVISION. 
      WORKING-STORAGE SECTION. 
      01 RANDOMRESULT PIC S9V9(10). 
  
      01 WS-CURRENT-DATE-DATA. 
      05 WS-CURRENT-DATE. 
       10 WS-CURRENT-YEAR PIC 9(04). 
       10 WS-CURRENT-MONTH PIC 9(02). 
       10 WS-CURRENT-DAY PIC 9(02). 
      05 WS-CURRENT-TIME. 
      10 WS-CURRENT-HOURS  PIC 9(02). 
      10 WS-CURRENT-MINUTE  PIC 9(02). 
      10 WS-CURRENT-SECOND  PIC 9(02). 
      10 WS-CURRENT-MILLISECONDS COMP-2. 
  05 WS-DIFF-FROM-GMT  PIC S9(04). 
  
      PROCEDURE DIVISION. 
      PRGRM. 
  
      PERFORM 4 TIMES 
      MOVE FUNCTION CURRENT-DATE TO WS-CURRENT-DATE-DATA 
      COMPUTE RANDOMRESULT = FUNCTION RANDOM (WS-CURRENT-MILLISECONDS) 
      DISPLAY "Seed value: " WS-CURRENT-MILLISECONDS UPON SYSOUT 
      DISPLAY "Random result: " RANDOMRESULT UPON SYSOUT 
      END-PERFORM 
  
      STOP RUN. 
  

輸出示例：

Seed value: 8.222829361429599E-67 
Random result: 0.6734141422 
Seed value: 8.964670591567083E-67 
Random result: 0.6734141422 
Seed value: 9.335591206635825E-67 
Random result: 0.6734141422 
Seed value: 9.335591206635825E-67 
Random result: 0.6734141422 

如果你對我的接近原來的問題（包括創建的字母數字字符的隨機密碼）的建議，我會很高興聽到它好。

編輯： 通過省略種子，這兩個問題都立即修復。更多背後的結論可以在下面的評論中找到。如果有人解釋爲什麼不同的種子仍然具有相同的價值，我很樂意聽到它！

Answer 1

是的，你的種子需要是一個整數，所以你不能使用COMP-2。種子不需要是一個特定的大小，只是一個整數，你可能會使它非常大。

程序編譯所花費的時間與任何事情無關。

您應該在第一次調用函數時指定SEED。之後，使用零。這將遵循「僞隨機」序列。你不需要每次「種子」，所以不需要擔心毫秒。

您應該始終輸出您的種子，以便您可以在以後重新生成序列。使用時間會變得很棘手，因此改爲使用包含種子的參數或單個記錄文件。

Answer 2

從this post，似乎RANDOM功能需要採取一個32位整數作爲種子。但是，您聲明WS-CURRENT-MILLISECONDS爲COMP-2浮點數（在其他語言中爲64位雙精度浮點數）。

我想這會使它成爲種子的無效參數，因此使用默認種子值0，或者只使用double的第一個或最後32位，所以您基本上得到part of the mantissa or significand對於你正在嘗試的數字是一樣的。

如果第一件事情發生，嘗試使用0作爲種子，我想你會得到相同的輸出。無論如何，你可以嘗試使用一些不同的整數進行播種，看看會發生什麼。

Answer 3

這裏有一些源代碼來產生隨機數希望這有助於。

IDENTIFICATION DIVISION. 
    PROGRAM-ID. RANDGEN as "ConsoleApplication2.RANDGEN". 
    AUTHOR. Myron D Denson. 
    DATE-COMPILED. 
    * ************************************************************** 
    * SUBROUTINE TO GENERATE RANDOM NUMBERS THAT ARE GREATER THAN 
    * ZERO AND LESS OR EQUAL TO THE RANDOM NUMBERS NEEDED WITH NO 
    * DUPLICATIONS. (CALL "RANDGEN" USING RANDGEN-AREA.) 
    *  
    * FORMULA CYCLES THROUGH EVERY NUMBER OF 2X2 ONLY ONCE. 
    * RANDOM-NUMBERS FROM 1 TO RANDOM-NUMBERS-NEEDED ARE CREATED 
    * AND PASSED BACK TO YOU. 
    * 
    * RULES TO USE RANDGEN: 
    * 
    * RANDOM-NUMBERS-NEEDED > ZERO 
    *  
    * COUNT-OF-ACCESSES MUST = ZERO FIRST TIME USED. 
    *   
    * RANDOM-NUMBER = ZERO, WILL BUILD A SEED FOR YOU 
    * WHEN COUNT-OF-ACCESSES IS ALSO = 0 
    *  
    * RANDOM-NUMBER NOT = ZERO, WILL BE NEXT SEED FOR RANDGEN 
    * YOU CAN PASS RANDGEN YOUR OWN RANDOM-NUMBER SEED 
    *  THE FIRST TIME YOU USE RANDGEN. 
    *  
    * BY PLACING A NUMBER IN RANDOM-NUMBER FIELD 
    *  THAT FOLLOWES THESE SIMPLE RULES: 
    *  IF COUNT-OF-ACCESSES = ZERO AND 
    *  RANDOM-NUMBER > ZERO. 
    *  
    * YOU CAN PICK THE SEED OR YOU CAN LET RANDGEN BUILD A SEED FOR YOU. 
    * 
    *  IF YOU PICK A SEED < RANDON-NUMBERS-NEEDED IT WILL BECOME THE LAST 
    *   RANDON-NUMBER YOU RECEIVE BACK. 
    *  IF SEED > RANDON-NUMBERS-NEEDED LAST NUMBER COULD BE ANYTHING.   
    *  
    *  THAT FOLLOWES THESE SIMPLE RULES: 
    *  IF COUNT-OF-ACCESSES = ZERO AND 
    *  RANDOM-NUMBER = ZERO AND 
    *  RANDOM-NUMBER-NEEDED > ZERO 
    *   
    *  TO INSURING A DIFFERENT PATTERN OF RANDOM NUMBERS 
    *  A LOW-RANGE AND HIGH-RANGE IS USED TO BUILD 
    *  RANDOM NUMBERS. 
    *  COMPUTE LOW-RANGE = 
    *    ((SECONDS + HOURS + MINUTES + MS) * 1753).   
    *  A HIGH-RANGE = RANDOM-NUMBERS-NEEDED + LOW-RANGE 
    *  AFTER RANDOM-NUMBER-BUILT IS CREATED 
    *  AND IS BETWEEN LOW AND HIGH RANGE 
    *  RANDUM-NUMBER = RANDOM-NUMBER-BUILT - LOW-RANGE 
    *    
    * **************************************************************   
    ENVIRONMENT DIVISION. 
    INPUT-OUTPUT SECTION. 
    FILE-CONTROL. 
    DATA DIVISION. 
    FILE SECTION. 
    WORKING-STORAGE SECTION. 
    01 WORK-AREA. 
     05 X2-POWER      PIC 9  VALUE 2. 
     05 2X2       PIC 9(12) VALUE 2. 
     05 RANDOM-NUMBER-BUILT   PIC 9(12) COMP. 
     05 FIRST-PART     PIC 9(12) COMP. 
     05 NOT-USED-NUMBER    PIC 9(12) COMP. 
     05 LOW-RANGE     PIC 9(12) VALUE ZERO. 
     05 HIGH-RANGE     PIC 9(12) VALUE ZERO. 
     05 YOU-PROVIDE-SEED    PIC X  VALUE SPACE. 
     05 RUN-AGAIN     PIC X  VALUE SPACE. 
     05 PAUSE-FOR-A-SECOND   PIC X  VALUE SPACE. 
    01 SEED-TIME. 
     05 HOURS      PIC 99. 
     05 MINUTES      PIC 99. 
     05 SECONDS      PIC 99. 
     05 MS       PIC 99. 
    * 
    * LINKAGE SECTION. 
    * Not used during testing 
    01 RANDGEN-AREA. 
     05 COUNT-OF-ACCESSES   PIC 9(12) VALUE ZERO. 
     05 RANDOM-NUMBERS-NEEDED  PIC 9(12) VALUE ZERO. 
     05 RANDOM-NUMBER    PIC 9(12) VALUE ZERO. 
     05 RANDOM-MSG     PIC X(60) VALUE SPACE. 
    *  
    * PROCEDURE DIVISION USING RANDGEN-AREA. 
    * Not used during testing 
    * 
    PROCEDURE DIVISION. 
    100-RANDGEN-EDIT-HOUSEKEEPING. 
     MOVE SPACE TO RANDOM-MSG. 
     IF RANDOM-NUMBERS-NEEDED = ZERO 
     DISPLAY 'RANDOM-NUMBERS-NEEDED ' NO ADVANCING 
     ACCEPT RANDOM-NUMBERS-NEEDED. 
     IF RANDOM-NUMBERS-NEEDED NOT NUMERIC 
     MOVE 'RANDOM-NUMBERS-NEEDED NOT NUMERIC' TO RANDOM-MSG 
      GO TO 900-EXIT-RANDGEN. 
     IF RANDOM-NUMBERS-NEEDED = ZERO 
     MOVE 'RANDOM-NUMBERS-NEEDED = ZERO' TO RANDOM-MSG 
      GO TO 900-EXIT-RANDGEN. 
     IF COUNT-OF-ACCESSES NOT NUMERIC 
     MOVE 'COUNT-OF-ACCESSES NOT NUMERIC' TO RANDOM-MSG 
      GO TO 900-EXIT-RANDGEN. 
     IF COUNT-OF-ACCESSES GREATER THAN RANDOM-NUMBERS-NEEDED 
     MOVE 'COUNT-OF-ACCESSES > THAT RANDOM-NUMBERS-NEEDED' TO RANDOM-MSG 
      GO TO 900-EXIT-RANDGEN. 
     IF YOU-PROVIDE-SEED = SPACE AND RANDOM-NUMBER = ZERO 
     DISPLAY 'DO YOU WANT TO PROVIDE SEED Y OR N: ' 
      NO ADVANCING 
      ACCEPT YOU-PROVIDE-SEED. 
     IF RANDOM-NUMBER = ZERO AND 
      (YOU-PROVIDE-SEED = 'Y' OR 'y') 
     DISPLAY 'ENTER SEED ' NO ADVANCING 
     ACCEPT RANDOM-NUMBER. 
     IF RANDOM-NUMBER NOT NUMERIC 
     MOVE 'RANDOM-NUMBER NOT NUMERIC' TO RANDOM-MSG 
     GO TO 900-EXIT-RANDGEN. 
    200-RANDGEN-DATA-HOUSEKEEPING.  
     MOVE FUNCTION CURRENT-DATE (9:8) TO SEED-TIME. 
     IF COUNT-OF-ACCESSES = ZERO 
     COMPUTE LOW-RANGE = 
       ((SECONDS + HOURS + MINUTES + MS) * 1753). 
     COMPUTE RANDOM-NUMBER-BUILT = RANDOM-NUMBER + LOW-RANGE. 
     COMPUTE HIGH-RANGE = RANDOM-NUMBERS-NEEDED + LOW-RANGE. 
     MOVE X2-POWER TO 2X2.    
    300-SET-2X2-DIVISOR. 
     IF 2X2 < (HIGH-RANGE + 1) 
      COMPUTE 2X2 = 2X2 * X2-POWER 
      GO TO 300-SET-2X2-DIVISOR.  
    * *********************************************************   
    * IF FIRST TIME THROUGH AND YOU WANT TO BUILD A SEED. * 
    * ********************************************************* 
     IF COUNT-OF-ACCESSES = ZERO AND RANDOM-NUMBER = ZERO 
      COMPUTE RANDOM-NUMBER-BUILT = 
       ((SECONDS + HOURS + MINUTES + MS) + HIGH-RANGE). 
    * *********************************************  
    * END OF BUILDING A SEED IF YOU WANTED TO * 
    * ********************************************* 
    * ******************************************************* 
    * THE NEXT 4 LINE OF CODE ARE FOR TESTING ON CONSOLE * 
    * *******************************************************    
    * IF COUNT-OF-ACCESSES = ZERO   
    *  DISPLAY 'SEED TIME ' SEED-TIME 
    *   ' RANDOM-NUMBER-BUILT ' RANDOM-NUMBER-BUILT 
    *   ' LOW-RANGE ' LOW-RANGE.   
    * *************************************************** 
    * THIS PROCESS IS WHERE THE RANDOM-NUMBER IS BUILT * 
    * *************************************************** 
    400-RANDGEN-FORMULA. 
     COMPUTE FIRST-PART = (5 * RANDOM-NUMBER-BUILT) + 7. 
     DIVIDE FIRST-PART BY 2X2 GIVING NOT-USED-NUMBER 
     REMAINDER RANDOM-NUMBER-BUILT. 
     IF RANDOM-NUMBER-BUILT > LOW-RANGE AND 
      RANDOM-NUMBER-BUILT < (HIGH-RANGE + 1) 
     GO TO 600-RANDGEN-CLEANUP. 
     GO TO 400-RANDGEN-FORMULA. 
    * *********************************************  
    * GOOD RANDOM NUMBER HAS BEEN BUILT  *    
    * ********************************************* 
    600-RANDGEN-CLEANUP. 
     ADD 1 TO COUNT-OF-ACCESSES. 
     COMPUTE RANDOM-NUMBER = 
      RANDOM-NUMBER-BUILT - LOW-RANGE. 
    * ******************************************************* 
    * THE NEXT 3 LINE OF CODE ARE FOR TESTING ON CONSOLE * 
    * ******************************************************* 
     DISPLAY RANDOM-NUMBER. 
     IF COUNT-OF-ACCESSES < RANDOM-NUMBERS-NEEDED 
     GO TO 100-RANDGEN-EDIT-HOUSEKEEPING.  
    900-EXIT-RANDGEN. 
     IF RANDOM-MSG NOT = SPACE 
     DISPLAY 'RANDOM-MSG: ' RANDOM-MSG. 
     MOVE ZERO TO COUNT-OF-ACCESSES RANDOM-NUMBERS-NEEDED RANDOM-NUMBER. 
     MOVE SPACE TO YOU-PROVIDE-SEED RUN-AGAIN. 
     DISPLAY 'RUN AGAIN Y OR N ' 
     NO ADVANCING. 
     ACCEPT RUN-AGAIN. 
     IF (RUN-AGAIN = 'Y' OR 'y') 
     GO TO 100-RANDGEN-EDIT-HOUSEKEEPING. 
     ACCEPT PAUSE-FOR-A-SECOND. 
     GOBACK.