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Справка Scilab >> Основные функции > &, &&

&, &&

Binary AND between integers. Logical AND over/between booleans and numbers

Syntax

Element-wise operator:

intMat = intA & intB
tfMat = A & B

and()-like short-circuited evaluation:

tf = U && V
if (U && V) then ... end
if (U & V)  then ... end
while (U && V) then ... end
while (U & V) then ... end

Arguments

intA, intB

Arrays of encoded integers of any inttype.

intA and intB must have the same sizes to be processed element-wise. If intA or intB is a scalar, it is priorly replicated to the size of the other operand before processing.

If intA and intB have not the same integer inttype, the operand with the smaller encoding is converted to the wider according to the following ranks: int8 < uint8 < int16 < uint16 < int32 < uint32 < int64 < uint64.

intMat

Array of encoded integers with the same sizes of intA and intB, and of the wider inttype of both (see hereabove). For any index i, intMat(i) = bitand(intA(i), intB(i)) intA & [] and [] & intA return the boolean array intA~=0.

A, B

Arrays of booleans or of numbers: encoded integers of any inttype, real or complex numbers. A and B may have distinct types, and may be one or both sparse-encoded. The special case where A and B are both encoded integers is excluded (see here-above).

A and B must have the same sizes to be processed element-wise. If A or B is a scalar, it is priorly replicated to the size of the other operand before processing.

tfMat

Boolean array with the same sizes of A and B. If A or B is sparse-encoded, so is tfMat.

For any index i, tfMat(i) is %T if neither A(i) nor B(i) are %F or zero. Otherwise, tfMat(i) is set to %F. A & [] and [] & A return [].

U, V

Arrays of full or sparse-encoded booleans or of numbers of any types and encoding: any inttype of encoded integers, full or sparse-encoded real or complex numbers.

U and V may have distinct data types, number of dimensions, and sizes.

tf

single boolean: Set to and(U) & and(V), without evaluating and(V) if and(U) is false (this is why the && operator is so-called short-circuited).

See and() for the definition of the evaluation to false depending on type and encoding.

Description

&&

For any boolean or numerical operands U and V, G = U && V is equivalent to if ~and(U), G = %F, else G = and(V), end.

• U and V may have distinct sizes or numbers of dimensions.
• The result is always a single boolean.
• and(V) is evaluated only if and(U) is true. This mainly avoids yielding errors when further operations with V are meaningless or prone to error when U is false. See examples.

&

When the & operator is used inside a logical condition tested by a while or by an if control structure, it is equivalent to the && operator (see above).

Otherwise, & has two different actions:

1. When both operands are encoded integers, intA & intB is processed element-wise and yields an array of integers resulting from the bitwise AND between corresponding components.
2. Otherwise, when operands are arrays of numbers or/and booleans, they are still processed element-wise. Provided that null numbers are equivalent to false booleans, the result is an array of booleans.

Comparing & and && with bitand() and and() :

• and(A) is equivalent to A && %T, whereas and(A, side) has no equivalence with &&.
• intA & intB accepts negative integers, while bitand(intA, intB) does not. bitand(A,B) works bitwise with decimal-encoded integers. The overloading code for & and && operators is h. %nan is true. A constant polynomial or rational is not considered as a number and is not an acceptable operand for & or &&.

Examples

A = [0 1; 1 0];   // equivalent to [%f %t ; %t %f]
B = [1 1; 0 0];   // equivalent to [%t %t ; %f %f]
spA = sparse(A);
spB = sparse(B);
spbA = sparse(A<>0);
spbB = sparse(B<>0);
iA = int8(A);
iB = int8(B);
cA = A + 0*%i;
cB = B + 0*%i;

// & as logical operation
A & B
A & spB    // Result is sparse encoded
iA & spB   // Result is sparse encoded
cA & iB
A & %nan   // %nan is %t

// & as bitwise operation
iA & iB

Ai8 = int8([ -1, 1; 127, -128]);
// Integer representation of Ai8:
// [ 1111 1111, 0000 0001 ;
//   0111 1111, 1000 0000 ]

Bi8 = int8([-2, 0; 126, -127]);
// Integer representation of Bi8:
// [ 1111 1110, 0000 0000 ;
//   0111 1110, 1000 0001 ]

Ai8 & Bi8

// Integer promotion
Ai16 = int16(Ai8);
Bui32 = uint32(Bi8);

r = Ai16 & Bui32, typeof(r)

// Shorted & or &&:
// ----------------
function res=foo()
error("foo() shall not be called")
endfunction

// & (simple) is always shorted in any if's condition:
if  %F & foo() then
// foo() is not called and this is not executed
end

A && foo()    // A, iA and cA have at least one element equals to 0.
iA && foo()   // Therefore, foo() is not called
cA && foo()

iA && iB // iA is evaluated as false resulting in the short-circuited operation

Avoiding conditional errors in or out of "if" and "while" conditions:

A = [ 1 3 -2 ; 4 -1  2]
c = issquare(A) & det(A)~=0
// det(A) is evaluated despite issquare(A) is false (so c is false anyway)
// But A should be square to be able to compute its det(). This leads to the error

// Now, we use the short-circuited && :
// det(A) is NO LONGER computed, since issquare(A) is false => anyway c is false
c = issquare(A) && det(A)~=0      // ==> no error

// In an "if" (or "while") tested condition, & is equivalent to &&
if issquare(A) & det(A)~=0      // => no error: here & is meant as &&
B = inv(A)
else
disp("A is not square")
end
--> A = [ 1 3 -2 ; 4 -1  2]
A  =
1.   3.  -2.
4.  -1.   2.

--> c = issquare(A) & det(A)~=0
det: Wrong type for input argument #1: Square matrix expected.

--> c = issquare(A) && det(A)~=0
c  =
F

--> if issquare(A) & det(A)~=0        // => no error: here & is meant as &&
>    B = inv(A)
> else
>    disp("A is not square")
> end

A is not square

Constant polynomials or rationals can't be processed with & or &&:

p = 1 + 0*%z
typeof(p)
p & 1
--> p = 1 + 0*%z
p  =
1

--> typeof(p)
ans  =
polynomial

--> p & 1
Undefined operation for the given operands.

• and — logical AND between the elements of a boolean or numerical array
• bitand — bitwise logical AND between element-wise integers of 2 arrays
• or operator (|) — Binary OR between integers. Logical OR over/between booleans and numbers
• not ~ — (~) логическое НЕ
• if — ключевое слово для условного выполнения
• while — ключевое слово while

History

 Версия Описание 6.0 && operator added