EVAL

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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