Programmer Guide/Command Reference/EVAL Intro/EVAL: Difference between revisions

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The <code>EVAL</code> command can be used to evaluate numerical expressions. These expressions can be constants, scalar variables, vectors, matrices or <code>[[Programmer Guide/Command Reference/EVAL/EVAL Subcommands|EVAL]]</code>[[Programmer Guide/Command Reference/EVAL_Intro/EVAL Subcommands| subcommands]].
The <code>EVAL</code> command can be used to evaluate numerical expressions. These expressions can be constants, scalar variables, vectors, matrices or <code>[[Programmer Guide/Command Reference/EVAL/EVAL Subcommands|EVAL]]</code>[[Programmer Guide/Command Reference/EVAL_Intro/EVAL Subcommands| subcommands]].
// 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.


<pre>
== Syntax ==
// 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.
</pre>
Syntax
 
An <code>EVAL</code> command uses the following general syntax:
An <code>EVAL</code> command uses the following general syntax:
 
<code>result := eval expression</code>
<code>result := eval expression</code>
<code>result := evalcheck expression</code>
 
An expression may be either a numerical expression, e.g.
<code>result := evalcheck expression</code>
<code>result := eval (5 * 10) % 3</code>
 
An expression can be either a numerical expression, e.g.
 
<code>result := eval (5 * 10) % 3</code>
 
or a subcommand, e.g.
or a subcommand, e.g.
 
<code>result := eval init(10,1,1)</code>
<code>result := eval init(10,1,1)</code>
 
or a combination thereof:
or a combination thereof:
 
<code>result := eval 5+max(fill(6,1,1))</code>
<code>result := eval 5+max(fill(6,1,1))</code>


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


Numerical and Logical Operators
=== Numerical Comparison Operators ===
 
The <code>EVAL</code> command supports the following numerical operators:


The <code>EVAL</code> command supports the following numerical comparison operators:
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Note that two numbers/vectors/matrices are considered equal if (and only if)
Note that two numbers/vectors/matrices are considered equal if (and only if)
# their dimensions are the same; and
# all elements are numerically equal.


(a) their dimensions are the same; and
=== Logical Operators ===
(b) all elements are numerically equal.
 
The <code>EVAL</code> command also supports the following logical operators:


The <code>EVAL</code> command supports the following logical operators:
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A C<nowiki>-</nowiki>like '<code>? :'</code> operator is also supported:
A C<nowiki>-</nowiki>like '<code>? :'</code> operator is also supported:
 
<code>result := eval 1 < 2 ? 1+2 : 1-2 // result is 3</code>
<code>result := eval 1 < 2 ? 1+2 : 1-2 // result is 3</code>
 
Note that unlike C, nested uses of this operator must be surrounded by brackets, e.g.:
Note that unlike C, nested uses of this operator must be surrounded by brackets, e.g.:
<code>result := eval 1 > 2 ? (5 == 5 ? 5 : 0) : (4 == 5 ? 3 : 4) // returns 4</code>


<code>result := eval 1 > 2 ? (5 == 5 ? 5 : 0) : (4 == 5 ? 3 : 4) // returns 4</code>
=== Examples ===
 
Examples
 
See the script <code>eval_examples.sts</code> for an extensive list of examples.
See the script <code>eval_examples.sts</code> for an extensive list of examples.


Command History
=== Version History ===
 
The <code>EVAL</code> command was added to the S_TOOLS-STx language in version 3.7.0. The <code>EVAL</code> command replaces and extends the <code>EVALUATE</code> command. If the <code>EVAL</code> 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 [[Programmer Guide/Command Reference/EVAL/Numerical objects|numerical objects]] than just the scalars <code>INT</code> and <code>NUM</code>.
The <code>EVAL</code> command was added to the S_TOOLS-STx language in version 3.7.0. The <code>EVAL</code> command replaces and extends the <code>EVALUATE</code> command. If the <code>EVAL</code> 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 [[Programmer Guide/Command Reference/EVAL/Numerical objects|numerical objects]] than just the scalars <code>INT</code> and <code>NUM</code>.
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Revision as of 20:56, 22 March 2011

The EVAL command can be used to evaluate numerical expressions. These expressions can be constants, scalar variables, vectors, matrices or EVAL subcommands. 

// 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
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 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 '? :' 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) // returns 4

Examples

See the script eval_examples.sts for an extensive list of 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.

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