Extrapolation Accuracy (XAC) File

You can use the XAC file to estimate how accurate individual results are. The report has a complex format, which the GEMPACK documentation explains.

An XAC file will not be produced unless the line:

Extrapolation accuracy file = YES ;

appears in your CMFSTART file (see below).

Sometimes, apparently poor accuracy is nothing to worry about. Suppose you have three variables, related by the identity:

(A)	Saving	=	Earning -	Spending
Solution 1	2	=	1000001-	999999
Solution 2	-2	=	999999-	1000001

GEMPACK estimates accuracy by comparing two extrapolated solutions (solution 1, solution 2). In this case we might conclude that the results for Earning and Spending were accurate to about 2 parts in a million (5 figures). For Saving we dont even know the sign of the result. But, in the context of Equation (A) and given the relative magnitudes of the variables, that is no cause for concern (pace Micawber). GEMPACK is not able to make use of economic insights or contextual information in reporting accuracy, and so some of the problems that it flags may be unimportant.

XAC file too large ?

WIth large models the XAC file can be rather large. You can replace the line:

Extrapolation accuracy file = YES ;

in your CMFSTART file in current version dir, with the line

Extrapolation accuracy file = NO ;

to have no XAC file.

Or, instead ADD to CMFSTART a line like:

XAC-retained %macro (REG)(TRAD_COMM)(TRAD_COMM,REG);

meaning that only variables of the dimensions listed will be kept in the XAC file.