[Maxima-bugs] [maxima:bugs] #3282 lsquares and lists of list of data to be fitted on

[Robert D. <rob...@us...>]

Yes, this is a bug in `lsquares_mse`. The problem is that it introduces a temporary variable and tries to assign the data to the temporary variable, but it is incorrect. I think I see how to fix it.


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** [bugs:#3282] lsquares and lists of list of data to be fitted on**

**Status:** open
**Group:** None
**Created:** Tue Jan 24, 2017 06:58 PM UTC by Gunter Königsmann
**Last Updated:** Tue Jan 24, 2017 06:58 PM UTC
**Owner:** nobody


I have a list of data sets that are huge => running lsquares_estimates() on them to fit them on an equation would need too big amounts of time.

Normally lsquares_estimates_approximate() helps in this case as it skips the step that tries to find an exact solution. But as I have not a single data set, but a list of data sets that somehow backfires:

~~~
(%i34)	load("lsquares");
	data:[
	    matrix([0,0],[1,1],[2,2]),
	    matrix([2,2],[1,1],[2,2])
	];
	eqtn:y=a*x^2+b*x+c;
	lsquares_mse(data[1],[x,y],eqtn);
	lsquares_estimates_approximate(%,[a,b,c]);
(%o30)	"/usr/local/share/maxima/branch_5_39_base_66_gbbb452f/share/lsquares/lsquares.mac"
(data)	[matrix(
		[0,	0],
		[1,	1],
		[2,	2]
	),matrix(
		[2,	2],
		[1,	1],
		[2,	2]
	)]
(eqtn)	y=a*x^2+b*x+c
(%o33)	sum((m6[i,2]-a*m6[i,1]^2-b*m6[i,1]-c)^2,i,1,1)
	Maxima encountered a Lisp error:
	 The value
	   ((MTIMES SIMP) -2.0
	    ((MEXPT SIMP) ((MQAPPLY SIMP ARRAY) (($DATA SIMP ARRAY) 1) 1 1) 2)
	    ((MPLUS SIMP) -1.0
	     ((MTIMES SIMP) -1.0 ((MQAPPLY SIMP ARRAY) (($DATA SIMP ARRAY) 1) 1 1))
	     ((MTIMES SIMP) -1.0
	      ((MEXPT SIMP) ((MQAPPLY SIMP ARRAY) (($DATA SIMP ARRAY) 1) 1 1) 2))
	     ((MQAPPLY SIMP ARRAY) (($DATA SIMP ARRAY) 1) 1 2)))
	 is not of type
	   DOUBLE-FLOAT.
	Automatically continuing.
To enable the Lisp debugger set *debugger-hook* to nil.
~~~

Only running lsquares_estimates on a single entry of the list works:

~~~
(%i29)	load("lsquares");
	data:matrix([0,0],[1,1],[2,2]);
	eqtn:y=a*x^2+b*x+c;
	lsquares_mse(data,[x,y],eqtn);
	lsquares_estimates_approximate(%,[a,b,c]);
(%o25)	"/usr/local/share/maxima/branch_5_39_base_66_gbbb452f/share/lsquares/lsquares.mac"
(data)	matrix(
		[0,	0],
		[1,	1],
		[2,	2]
	)
(eqtn)	y=a*x^2+b*x+c
(%o28)	sum((data[i,2]-a*data[i,1]^2-b*data[i,1]-c)^2,i,1,3)/3
	*************************************************
	  N=    3   NUMBER OF CORRECTIONS=25
	       INITIAL VALUES
	 F=  1.000000000000000D+01   GNORM=  1.753726191728787D+01
	*************************************************
	   I  NFN     FUNC                    GNORM                   STEPLENGTH
	   1    2     2.796937667198332D-01   1.961076084276657D+00   5.702144409522791D-02  
	   2    3     1.464269617620298D-01   4.983306664572200D-01   1.000000000000000D+00  
~~~
---snip---
~~~
	  13   14     3.397773998012277D-06   4.742450181229817D-03   1.000000000000000D+00  
	  14   15     2.643557109421608D-08   2.597101638571121D-04   1.000000000000000D+00  
	 THE MINIMIZATION TERMINATED WITHOUT DETECTING ERRORS.
	 IFLAG = 0
(%o29)	[[a=-3.405898581949557*10^-4,b=1.000676542954337,c=-1.342533507359797*10^-4]]
~~~

I have been able to ship around this problem by putting the data set I am working on into a temporary variable before running lsquares:

~~~
load("lsquares");
data:[
    matrix([0,0],[1,1],[2,2]),
    matrix([2,2],[1,1],[2,2])
];
eqtn:y=a*x^2+b*x+c;
makelist(block([tmp],
        tmp:data[i],
        lsquares_estimates_approximate(lsquares_mse(tmp,[x,y],eqtn),[a,b,c])
    ),
    i,1,length(data)
);

...but I am convinced that the fact that I needed this is a bug.
~~~



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