Sym Input File Syntax

Input files consist of: set, parameter and variable declarations, and equations. All statements must end with a semicolon. Anything from a // to the end of the line is taken to be a comment and is ignored. Items in square brackets are optional and may be omitted. Attributes are target-language dependent: there are no attributes applicable to all languages.

Set Declarations:

Set elements do not need to be unique as long as sets using the same element names cannot be mistaken for subsets of each other. For example, elements a and b will distinct in set1(a,b,c) and set2(a,b,d). However, using an additional set3(a,b) should be avoided and will be flagged as an error in subsequent versions of sym.

SET name (elements)              ['description'] ;
SET name = prevset               ['description'] ;
SET name = prevset(elements)     ['description'] ;
SET name = prevset + (elements)  ['description'] ;
SET name = prevset - (elements)  ['description'] ;
SET name = prevset + otherset    ['description'] ;
SET name = prevset - otherset    ['description'] ;
SET name = UNION(setlist)        ['description'] ;

Variable and Parameter Declarations:

PARAMETER name [(sets)]   ['description'] [attributes] ;
VARIABLE  name [(sets)]   ['description'] [attributes] ;

Equations:

[EQUATION name|/name/] [sets:] expr = expr ['description'] [attributes];
['description'] [EQUATION name|/name/] [sets:] expr = expr [attributes];

Expressions:

expr + expr
expr - expr
expr * expr
expr / expr
expr ^ expr
- expr
( expr )
function
lead(variable)
lag(variable)
variable
number

Variable References:

name
name#list
name(sets)
name(sets)#list

Functions:

EXP(expr)
LN(expr)
LOG(expr)
PROD(set,expr)
SUM(set,expr)

Notes on Output Targets:

The sections below provide additional information about the features or requirements of specific output targets.

debug

Write out in a format useful for checking equations.

• Equation descriptions will be written

html

Write out the model in HTML for use as documentation.

• Equation descriptions will be written

msgproc

Support the Ox implementation of the MSG/G-Cubed solution algorithm.

oxgs

Support a simple Ox implementation of the Gauss-Seidel algorithm.

oxgst

Extended version of the OxGS target that removes a restriction in OxGS limiting it to single periods.

oxnewton

Support an Ox implementation of Newton’s Method for simple models.

tablo

Support GEMPACK’s TABLO language.

• All variables are implicitly subscripted by time. However, parameters are not.

• The left side of an equation may be an expression, not just a variable name.

• At most one attribute is allowed in variable and parameter declarations. If present, it is used as the name of an HAR header and should have the form: c###.

• Parameters are read from TABLO logical name ‘param’. Variables are read from one of the following files depending on the value of the first letter of the header: B = ‘base’, K = ‘kalman’, M = ‘make’, N = ‘endog’, and X = ‘exog’. If the first letter does not match one of the above ‘base’ will be used as the file name.

troll

Support TROLL.