ARITHMETIC EXPRESSION AND OPERATORS IN PROLOG Artificial Intelligence

ARITHMETIC EXPRESSION AND OPERATORS IN PROLOG Artificial Intelligence Lab Md. Tarek Habib Department of Computer Science and Engineering Daffodil International University

ARITHMETIC EXPRESSION AND OPERATORS Arithmetic Evolution: Simple arithmetic operators such as ( + or * ) are valid Prolog atoms. Therefore, expressions like +(3, 5) are valid Prolog terms. They can also be written as infix operators , like in 3+5.

ARITHMETIC EXPRESSION AND OPERATORS Arithmetic Evolution: Without specifically telling Prolog that we are interested in the arithmetic properties of such a term, these expressions are treated purely syntactically i. e. their values are not evaluated. That means, using ( = ) won’t work the way that you might have expected.

ARITHMETIC EXPRESSION AND OPERATORS Arithmetic Evolution: Example: ? - 3 + 5 = 8. False. Here, the term 3+5 and 8 don’t match, the former is compound term whereas the letter is a number

ARITHMETIC EXPRESSION AND OPERATORS Arithmetic Evolution: (is) Operator To check the result, we first have to tell Prolog to arithmetically evaluate the term ( 3 + 5 ). This is done by using built-in operator (is). Example: ? - 8 is 3+5. True. Again, we can match by the variable with another number. ? - X is 3+5 , X = 8.

ARITHMETIC EXPRESSION AND OPERATORS Arithmetic Evolution: (is) Operator Again, We can query like, ? - X is 3+5. X=8 If we write like, ? - 3+5 is X False. Because, is only cause the argument to it’s right and tries to match the result with the left hand argument.

ARITHMETIC EXPRESSION AND OPERATORS Arithmetic Evolution: (is) Operator For Multiplication, ? - X is 3 * 8. X = 24. For Subtraction, ? - X is 3 - 5. X = -2 For Division, ? - X is 6/2. X=3 Use // for integer division.

ARITHMETIC EXPRESSION AND OPERATORS Predefined Arithmetic Functions and Relations: The arithmetic operators available in Prolog: v. Functions, v. Relations

ARITHMETIC EXPRESSION AND OPERATORS Functions: Consider an Expression like, 2 + ( -3. 2 * X – max ( 17, X ) ) / 2 * * 5 Here, max /2 expression evaluates to the largest of it’s two arguments and 2 * * 5 means 2 to the power 5.

ARITHMETIC EXPRESSION AND OPERATORS Some other Functions: vmin/2 ( minimum ) , vabs/1 ( absolute value ) , vsqrt/1 ( square root ) , vsin/1 ( sine ) , vround/1 ( round a float number to an integer) , vmod/2 ( module ). Can be used only on the right side is operator.

ARITHMETIC EXPRESSION AND OPERATORS Query with Functions: max/2: ? - X is max (2 , 4). X = 4. min/2: ? - X is min ( 2 , 4 ). X = 2. abs/1: ? - X is abs( 2. 4) X = 2. 4

ARITHMETIC EXPRESSION AND OPERATORS Query with Functions: sqrt/1: ? - X is sqrt( 4 ). X = 2. round/1: ? - X is round(2. 44). X = 2. mod/2: ? - X is mod(4 , 2). X = 0. ? - X is round(2. 64). X = 3. ? - X is mod(4 , 3). X = 1.

ARITHMETIC EXPRESSION AND OPERATORS Relations: Arithmetic relations are used to compare two evaluated arithmetic expressions. Example: The goal X > Y succeeds. if expression X evaluates to be a greater number than expression Y. (is) operator isn’t needed Arguments are evaluated whenever an arithmetic relation is used.

ARITHMETIC EXPRESSION AND OPERATORS Relations: Besides > (greater) the operator < (lower), Available operator are, v=< (lower or equal) , v>= (greater or equal) , v== (non equal) , v=: = (equal).

ARITHMETIC EXPRESSION AND OPERATORS Relations: The former compares two evaluated arithmetic expressions and later performs logical pattern matching. Example: Differentiation of =: = ? - 2 ** 3 =: = 3+5. and = is crucial. True. Again, False. Because the ? - 2 ** 3 =: = 2+5. matching returns False. false.

ARITHMETIC EXPRESSION AND OPERATORS Relations: ? - 2 ** 5 == 2+4. True ? - 2 ** 5 >= 2+4. True ? - 2 ** 5 =< 2+4. False.

END OF ARITHMETIC EXPRESSION AND OPERATORS THANK YOU!