Difference: LogicInAMPL (3 vs. 4)

Revision 42008-03-18 - TWikiAdminUser

Line: 1 to 1
 
META TOPICPARENT name="AMPLSyntax"
Added:
>
>
<-- Ready to Review -->
 

Logic in AMPL

  1. Relational Operators
Deleted:
<
<
  • Logical Expressions
  • Binary Parameters
  •  
  • Logical Operators
  • Added:
    >
    >
  • Logical Expressions
  •  
  • Conditional Expressions
  • Conditional Structures
  • Added:
    >
    >
  • Binary Parameters
  •  

    Relational Operators

    Line: 24 to 26
      Return to top
    Added:
    >
    >

    Logical Operators

    Logical operators are used to combine logical expressions. They are most commonly used in conditional statements, conditional structures and conditional loops. The logical operators are not, and and or. They are used as shown in the table below:

    Expression Result
    not <expression> True if <expression> is false, false if <expression> is true
    <e1> and <e2> True if <e1> and <e2> are both true, otherwise false
    <e1> or <e2> True if either <e1> or <e2> are true, otherwise false

    Return to top

     

    Logical Expressions

    Logical expressions are expressions that will evaluate to either true or false. Logical expressions are

    Changed:
    <
    <
    usually defined in terms of the relational operators:
    >
    >
    usually defined in terms of the relational operators:
     
    Lower[r] <= sum {i in INGREDIENTS} Contributes[r, i] * Amount[i]
    
    Line: 48 to 61
      Return to top
    Added:
    >
    >

    Conditional Expressions

    A conditional expression is very much like the IF function in Microsoft Excel:

    param ifvalue := if <some logical expression> then
                       <a value>
                    [else
                       <another value>];
    

    If the logical expression is true then ifvalue will be set to <a value>, otherwise it is set to 0 (by default) or, if the else part of the expression is present, <another value>. Note that if the else keyword is present, then no ; needs to be included after <a value>.

    Return to top

    Conditional Structures

    A conditional structure is the same as the classical if_-_then_-_else statement in programming languages like MATLAB, Fortran, Visual Basic and C++:

    if <logical expression> then
      <a statement>;
    [else
      <another statement>;]
    

    Note here that even if the else keyword is present you need to end <a statement> with ;. If you want to include more than one statement within the conditional structures you can use { and } to enclose your statements:

    if <logical expression> then
    {
      <some statements>
    }
    [else
    {
      <some other statements>
    }]
    

    Return to top

     

    Binary Parameters

    Changed:
    <
    <
    In AMPL we can create binary parameters by using the {\tt binary} keyword in the parameter declaration:

    \begin{verbatim}

    >
    >
    In AMPL we can create binary parameters by using the binary keyword in the parameter declaration:
    
    
     param stillSearching binary;
    Changed:
    <
    <
    \end{verbatim}

    Binary parameters are used in a similar way to boolean variables (in Matlab, C, etc) and logical variables (Fortran). If a binary parameter has the value 0 this is equivalent to false, and 1 is equivalent to true. Binary parameters can be used with conditional expressions to hold a true/false result from a logical expression:

    \begin{verbatim}

    >
    >

    Binary parameters are used in a similar way to boolean variables (in Matlab, C, etc) and logical variables (Fortran). If a binary parameter has the value 0 this is equivalent to false, and 1 is equivalent to true. Binary parameters can be used with conditional expressions to hold a true/false result from a logical expression:

    
    
     param isGreater binary;

    let isGreater := if 4 > 5 then 1 else 0; # isGreater = 0 (false) let isGreater := if 6 > 5 then 1; # else 0 is the default, isGreater = 1 (true)

    Changed:
    <
    <
    \end{verbatim}

    >
    >
     so the syntax is
    Changed:
    <
    <

    \begin{verbatim} \end{verbatim} or as the condition in a conditional statement or conditional structure. They are very useful for building complex conditional statements or structures:

    \begin{verbatim} Some example from depth first searching or column generation \end{verbatim}

    and controlling loops.

    Logical Operators

    <\tt not} {\tt and} {\tt or}

    Conditional Expressions

    A conditional expression is very much like the IF function in Excel: param ifvalue := if then [else ];

    >
    >
    let <binary parameter> := if <expression> then 1;
    
     
    Changed:
    <
    <
    If the logical expression is true then ifvalue will be set to , otherwise it is set to 0 (by default) or, if the else part of the expression is present, . Note that if the else keyword is present, then no ; needs to be included after .
    >
    >
    You can also set binary parameters within conditional structures
    binary <binary parameter>;
    
    
     
    Changed:
    <
    <

    Conditional Structures

    >
    >
    if <expression> then let <binary parameter> := 1; else let <binary parameter> := 0;
     
    Changed:
    <
    <
    A conditional structure is the same as the classical if-then-else statement in programming languages like MATLAB, Fortran, Visual Basic and C++: if then ; [else ;] Note here that even if the else keyword is present you need to end with ;. If you want to include more than one statement within the conditional structures you can use { and } to enclose your statements. if then { } [else { }]
    >
    >
    Binary parameters may be used in logical expressions or as the condition in a conditional statement or conditional structure. They are very useful for building complex conditional statements or structures:
    Some example from depth first searching or column generation
    
    and controlling conditional loops:
    Some example from depth first searching or column generation
    
     
    Added:
    >
    >
    Return to top
      -- TWikiAdminGroup - 18 Mar 2008 \ No newline at end of file
     
    This site is powered by the TWiki collaboration platform Powered by PerlCopyright © 2008-2021 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
    Ideas, requests, problems regarding TWiki? Send feedback