DM41 Save/Restore Statistics

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====== DM41 Save/Restore Statistics ======

** Using Extended Memory to save Statistics Registers **

===== Background =====

Statistics use 6 regular registers to keep track of data for calculating Mean and Standard Deviations.

Keeping a long-term record of a set of variables means not being able to use the Statistics functions for anything else unless steps are taken to save and restore the registers.

It is possible to save the 6 registers in a data file in Extended Memory and then use the statistics for other things, and restore the saved Statistics back to Main Memory when required.

By Default the Statistics registers start at **R11** but this can be changed with the command ''∑REG''

This is the default list of Statistics Registers and contents

|R11|∑x|Summation of x-values|
|R12|∑x<sup>2</sup>|Summation of squares of x-values.|
|R13|∑y|Summation of y-values.|
|R14|∑y<sup>2</sup>|Summation of squares of y-values.|
|R15|∑xy|Summation of products of x- and y-values.|
|R16|n|Number of data points accumulated.|

**Advantage Pac : CFIT application ** seems to reset ''∑REG'' to **12**

===== Extended Memory Data File =====

The statistics registers use 6 Main Memory registers, //**usually R11 -> R16**//

We need to create a Data File in Extended Memory to hold these.

  * Put the name in ''ALPHA'' e.g. ''REGS''
  * Put ''6'' in ''x'' register
  * excecute ''CRFLD'' to create the Data File ''REGS'' in Extended Memory

Once it's created it can be used to hold the contents of the 6 Statistics Registers

===== Save Registers to Extended Memory =====

  * We need to make sure our Data File is the current file and that the pointer is at the beginning of the file
    * Put ''REGS'' in ''ALPHA''
    * Put ''0'' in ''X'' so that we put the pointer at the first register record in the data file.
    * Execute ''SEEKPTA''
  * Now we need to copy the 6 Registers R11 -> R16 to the Data File ''REGS''
    * ensure ''REGS'' is still in ''ALPHA''
    * put a number in ''X'' to indicate which range of Registers to save, this is ''bbb.eee'' where ''b'' is the beginning register and ''e'' is the end
      * put ''11.016'' in ''X''
    * execute ''SAVERX''

===== Restore Registers from Extended Memory to Main Memory ====

  * We need to make sure our Data File is the current file and that the pointer is at the beginning of the file
    * Put ''REGS'' in ''ALPHA''
    * Put ''0'' in ''X'' 
    * Execute ''SEEKPTA''
  * We can copy the 6 registers held in the Data File ''REGS'' back to R11 -> R16
    * ensure ''REGS'' is still in ''ALPHA''
    * put a number in ''X'' to indicate where the recovered registers will be put in Main Memory 
      * put ''11.016'' in ''X''
    * execute ''GETRX''

===== A program to make it easier =====

It is possible to change the base register of the 6 Statistics Registers, away from the default of R11. 

We need to take this into account.

This uses the query ''∑REG?'' to find the base register, then create ''bbb.eee'' using simple arithmetic.

When used in ''SAVER'' (save''R''egs) we ensure we copy the current Statistics Registers data.

When used in ''GETR'' (get''R''egs) we ensure we restore our data to the Registers currently set to be the active Statistics Registers (they may have changed since first saving them)

<code>

LBL ¬SAVER
¬REGS
0
SEEKPTA
∑REG?
1.001
*
.005
+
SAVERX
¬REGS SAVED
AVIEW
PSE
CLD
RTN
LBL ¬GETR
¬REGS
0
SEEKPTA
∑REG?
1.001
*
.005
+
GETRX
¬REGS OK
AVIEW
PSE
CLD
RTN

</code>


===== Multiple Saved Files =====

It's possible to have more than one Extended Memory file with Stats registers.

This could keep track of different sets of statistics and allow restore, update, save for many sets of statistical data.

I've set up **two** data files : ''REGS'' and ''CHESS'' in extended memory and made **two** version of the simple program above, the only change is to alter the lines which put the name of the file in ''ALPHA''

Here is ''SAVEC'' and ''GETC'' for save''C''hess and get''C''hess

<code>

LBL ¬SAVEC
¬CHESS
0
SEEKPTA
∑REG?
1.001
*
.005
+
SAVERX
¬CHESS SAVED
AVIEW
PSE
CLD
RTN
LBL ¬GETC
¬CHESS
0
SEEKPTA
∑REG?
1.001
*
.005
+
GETRX
¬CHESS OK
AVIEW
PSE
CLD
RTN

</code>
===== Further Ideas =====

I might make a better version which prompts for a Data File name rather than having one separate program for each scenario


{{tag>calculator dm41x dm41l}}

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