Programmer Guide/Command Reference/EVAL

Introduction

The EVAL command can be used to evaluate numerical, vector, and matrix expressions. These expressions may be built up from numerical constants, from scalar, vector, and matrix variables, and from a large number of EVAL functions, and operators.

// if the variable #v does not exist then the following command
// assigns a table item to #v.
$#v := eval vv(1,2,3,4)
// if #v is a value item, then #v remains a value item.

Syntax

An EVAL command uses the following general syntax:

result := eval expression

or

result := evalcheck expression

An expression may be either a numerical expression, e.g.

result := eval (5 * 10) % 3

or a subcommand, e.g.

result := eval init(10,1,1)

or a combination thereof:

result := eval 5+max(fill(6,1,1))

If the expression is syntactically ill-formed, an error (EVAL) or warning (EVALCHECK) is reported. See the example script expression_check.sts for details.

Numerical Objects

The following numerical objects are known to the EVAL command. The fields of the table item table are all numeric (you can use a parameter table). The value item value can contain numbers, vectors or matrices. The wave item wave is any wave item.

syntax	description	data type
constantNumber	a scalar constant. E.g. 4.5 or 4	scalar
table	the content of the whole table	vector, matrix
table[i,*] table[i,]	the i-th row of the table	scalar, vector
table[*,j] table[,j]	the j-th column of the table	scalar, vector
table[i,j]	the value of the i-th row and j-th column of the table	scalar
value	the content of the value item	scalar, vector, matrix
value[i,*] value[i,]	the i-th row of the value item	scalar, vector
value[*,j] value[,j]	the j-the column of the value item	scalar, vector
value[i,j]	the value of the i-th row and j-th column of the value item	scalar
wave[!signal,*] wave[!signal,]	the signal from all channels	vector, matrix
wave[!signal,ch]	the signal from channel ch (=1,2,...)	vector
wave[!signal,*,b,l]	the signal from all channels from sample b to sample b+l-1	vector, matrix
wave[!signal,ch,b,l]	the signal from channel ch from sample b to sample b+l-1	vector

Numerical Comparison Operators

The EVAL command supports the following numerical comparison operators:

>	less than
<	greater than
<=	less than or equal to
>=	greater than or equal to
==	equal to
!=	not equal to

Note that two numbers/vectors/matrices are considered equal if (and only if)

1. their dimensions are the same; and
2. all elements are numerically equal.

Logical Operators

The EVAL command supports the following logical operators:

||	logical or
&&	logical and
!	unary not

A C-like '? :' selection operator is also supported:

result := eval 1 < 2 ? 1+2 : 1-2 // result is 3

Note that unlike C, nested uses of this operator must be surrounded by brackets, e.g.:

result := eval 1 > 2 ? (5 == 5 ? 5 : 0) : (4 == 5 ? 3 : 4) // result is 4

EVAL subcommands

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Examples

For an extensive list of examples, see the script eval_examples.sts: Programmer Guide/Command Reference/EVAL Examples/EVAL Examples

Version History

The EVAL command was added to the S_TOOLS-STx language in version 3.7.0. The EVAL command replaces and extends the EVALUATE command. If the EVAL command is not assigning to an existing item, a table is assigned. Note that the current maximum number of arguments is 64 (S_TOOLS-STx version 3.8.0). As of version 3.7.0, S_TOOLS-STx has more numerical objects than just the scalars INT and NUM.