Checking if sides of triangle are positive and if equality rule is satisfied.

So, I could easily do this using multiple if statements but that seems fairly repetitive. Is there an and or operator in MATLAB so that I could say: if a <= 0 and or b <= 0 and or c <= 0 error... end

And, then do a similar thing with the equality. Sorry for the fairly simple questions, first week or so using MATLAB.

Answer 1

[Matt J]

 if any([a,b,c]<=0)

[David]

Is there a vectorized command that compares the corresponding entries of vectors? Like, checking a matrix of [a + b, a + c, b + c] against one of [ c, b, a]? So that I can check that position 1 of matrix 1 is >= position 1 of matrix 2.

[Matt J]

All of the relational operators in MATLAB except for the short circuited ones are vectorized, e.g.,

>> [1,2,3]<=[5, 0, 6]

ans =

       1     0     1

[David]

If only one of them evaluates to true will the code in the if statement run? Or do all have to evaluate to true?

[Matt J]

Which if statement are you talking about? In the code I proposed for you, I use the any() command. As you can see if you read

 >> doc any

the output of any(X) is true if any X(i) is true.

[David]

Ok, I may have misunderstood so. Does the following code make sense?

function [a, b, c] = Heron(A, S)
if any([a, b, c]) <= 0 || [a + b, a + c, b + c] <= [c, b, a]
   error('Invalid selection of a, b or c or invalid combination of the three')
end

Thanks.

[Matt J]

No. It does not make sense.

[David]

Only the if statement obviously. Is there something in particular that's incorrect about it or is it just off the walls in general? Apologies for all the questions.

[Matt J]

I can't tell what it's attempting to test. That's what I meant when I said it doesn't make sense.

Aside from that, though, if you run it, you will get an error. The short-circuited logical operators "&&" and "||" only apply to scalar expressions, not vectors.

[David]

Gotcha. Just looked up the any()operation and I understand it now. Thanks.

Answer 2

[Image Analyst]

if a<=0 || b<=0 || c<=0
  % It's bad
end

[David]

This evaluates to true if more than one of the variables are less than 0? I was always under the impression that meant or exclusively, like 1 or the other but not both. Thanks.

[Matt J]

No. There is xor() for that

[David]

Btw, the above is a genuine question, not me trying to disprove you.

[David]

Thanks!