When use || and | in if?
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john
el 26 de Abr. de 2014
Hello,
when can I use and | in command if?
For example:
if a||b
if a| b
Thank you
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Azzi Abdelmalek
el 26 de Abr. de 2014
a||b will return 1 if the first expression a is true, without evaluating the second expression b
Example
2==2 || hhh % even hhh is not defined Matlab will not evaluate it, because the first expression 2==2 is true
a&&b will return 0 if the first expression a is false without evaluating the second expression b
6 comentarios
Azzi Abdelmalek
el 26 de Abr. de 2014
Editada: Azzi Abdelmalek
el 26 de Abr. de 2014
Because Matlab, in both case (| or | | ) evaluate the first expression h which is not defined.
Azzi Abdelmalek
el 26 de Abr. de 2014
It's better to use | |, this can make your code faster, when the first expression is true, Matlab doesn't need to evaluate the second one.
Más respuestas (1)
dpb
el 26 de Abr. de 2014
Depends entirely on the purpose...the double logical operators short-circuit and return only a scalar whereas the single ones are point-by-point operators over the full dimension of the two operands and return a matrix of the same size.
doc relop
has further details and info
2 comentarios
Jan
el 27 de Abr. de 2014
Editada: Jan
el 27 de Abr. de 2014
@John: When a and b are scalars, both versions are equivalent. But the first one || is slightly faster (nano-seconds for scalar operands...), when the first expression is true already. When a and/or b is a vector, you need the , which is equivalent to |or(a==3, b==2). But then the vector expression in the if command is tricky, because implicitly this is performed:
expr = or(a==3, b==2);
if all(expr) && ~isempty(expr) ...
This is at least confusing or can even be a bug, if this behavior is not intended.
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