if a & b

i tiped this condition if m <= 0 && i > 1 and matlab is blocking it and this is the error msg Operands to the and && operators must be convertible to logical scalar values. some one can help me ?

[Skander Marouani]

i solved the problem , i just replaced && by & and it works!!

[Stephen23]

"i solved the problem , i just replaced && by & and it works!!"

And then in two days you will come back and ask why the code inside the if is not being executed....

For reasons of code clarity you should avoid using vector/matrix conditions with if, while, etc, and always use a scalar condition using any, all, || and && as required. This will make your code easier to understand and less buggy.

[Skander Marouani]

i didn't understand what you want to say

[Stephen23]

@Skander Marouani: beginners are often confused by the behavior of non-scalar conditions for if, while, etc. You will find plenty of examples on this forum, e.g.:

https://www.mathworks.com/matlabcentral/answers/7164-using-conditional-and-in-if-statements

https://www.mathworks.com/matlabcentral/answers/387513-write-a-computer-program-that-finds-all-the-isolated-primes-between-50-and-100-do-not-use-matlab-s

https://www.mathworks.com/matlabcentral/answers/384233-true-false-results-to-be-saved-as-a-value#comment_538312

https://www.mathworks.com/matlabcentral/answers/330392-how-is-a-logical-array-evaluated-as-an-if-condition

https://www.mathworks.com/matlabcentral/answers/156302-if-condition-with-array-of-elements

etc, etc, etc. But luckily, as I wrote in my earlier comment, this confusion is trivial to avoid by simply only using scalar conditions, and using any, all, ||, and && as required, which make the code intent perfectly clear. So you should not swap && for & as you have done, but explicitly add any or all as fits your logical conditions.

[Guillaume]

Yes, as Stephen says you did not solve the problem. You got rid of the error by introducing a subtler problem which only occurs under some circumstance because you didn't actually understand the cause of the problem.

Chances are you will come across the new problem 5 minutes before an important deadline.

If you really want to solve the problem then you need to tell us:

- was it intended that m or i is a vector. If not, then that's the first bug you need to fix

- if it was intended, then you need to explain if the if applies when all the values are greater (or smaller) than the threshold or only some of them.

It's also very possible that the if is not even needed, depending on what you are doing.

Answer 1

[Greg]

This means m or i (or both) are not convertible to logical scalar values.

They could be not convertible to logical (is {'Hello World'} true or false?), or they aren't scalar (is [true, false, true, false] true or false?).

Also, your question title is explicitly different from your question. The commands a & b and a && b are drastically different.

Answer 2

[Roger Stafford]

You can't use the "short circuit" forms of logical operations for operands other than scalars. The double symbol '&&' is the short circuit form of '&'.