DM41X Curve Fitting - John's Vademecum

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====== DM41X Curve Fitting ======

<note>
The Advantage Pac CFIT program requires all data values to be positive/non-zero

This is quite limiting and perhaps a better method is the PPC ROM's **CV** program.

**CV** does the same curve fitting (including selecting the //best// fit ) without this restriction for curves where negative co-ordinates are appropriate.

It also gives the function of calculating an estimated **x** value from an entered **y**, which CFIT doesn't do.

[[ppc_cv]]

</note>

Advantage Pac functions for statistical curve fitting.

**CFIT** program provides the functions to fit statistics data to ''LIN'', ''Exp'', ''LOG'', ''Power'' and ''Best Fit''

<key>XEQ</key><key>ALPHA</key><key>'C'</key><key>F</key><key>I</key><key>T</key><key>ALPHA</key>

  * Save ''CFIT'' to a ''CST'' menu entry to make it easier to access

  * Clear Statistics Registers with <key>'C'</key> (''CLΣ'')
  * Enter Statistics in usual way with ''Y'', <key>'ENTER'</key>, ''X'', <key>'A'</key>(''Σ+'')
  * Don't use any data points ≤0
  * When all data pairs are entered press <key>'E'</key> (''FIT'')
  * Now choose which type of fit to use
    * ''L'' = Linear
    * ''LOG'' = Logarithmic
    * ''Ex'' = Exponential
    * ''P'' = Power
    * ''B'' = Best Fit
  * <key>R/S</key> to cycle through the coefficients of the curve fit ''a'', ''b'', ''R^2'' (error ratio)
  * You can next enter an ''x'' value to find the curve-fitted ''y'' value
  * pressing <key>R/S</key> can exit back to the Curves menu ''L LOG Ex P B'' to try a different fit to the same data
  * pressing <key>R/S</key> can exit back to the main menu to clear and enter a new set of data

=== Curve Fit values ===

  * Linear ''y = a + bx''
  * Ex ''y = ae<sup>bx</sup>''
  * Log ''y = a + b ln(x)''
  * Power ''y = a x<sup>b</sup>''

=== Example of a Best Fit (LOG) ===

| X |0.72|1.31|1.95|2.58|3.14|
| Y |2.16|1.61|1.16|0.85|0.5|


  * ''CFIT''
  * ''CLΣ''
  * ''2.16'' <key>ENTER</key> ''0.72'' <key>'A'</key> (''Σ+'')
  * ''1.61'' <key>ENTER</key> ''1.31'' <key>'A'</key> (''Σ+'')
  * ''1.16'' <key>ENTER</key> ''1.95'' <key>'A'</key> (''Σ+'')
  * ''0.85'' <key>ENTER</key> ''2.58'' <key>'A'</key> (''Σ+'')
  * ''0.5'' <key>ENTER</key> ''3.14'' <key>'A'</key> (''Σ+'')
  * <key>'E'</key> (''FIT'')
  * <key>'E'</key> (''B'') //best fit//
  * display : ''LOG''
  * <key>R/S</key>`
  * display : ''a = 1.8515''
  *  <key>R/S</key>`
  * display : ''b = -1.1021''
  * <key>R/S</key>`
  * display : ''r^2 = 0.9893''
  * <key>R/S</key>`
  * display : ''X=?''
    * enter an X value if wanted, to get a ''y''
    * ''1.5'' <key>R/S</key>
    * display : ''Y=1.4046''
    * <key>R/S</key>`
    * enter another, or press <key>R/S</key> again to exit to the curve fitting menu
  * try a different curve fit.... (''L'', ''Ex'' etc) or
  * <key>R/S</key> to exit to the top menu

the curve found is '' y = 1.8515 - 1.1021 ln(x)''
 

--- //John Pumford-Green 31/07/24 14:46 BST//


===== Further Information =====


{{tag>calculator dm41x}}

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