MATLAB Answers

Sarah
2

"Or Statement" using if operator

Asked by Sarah
on 2 Feb 2012
Latest activity Commented on by Aaron Eldridge on 28 Apr 2016
Hello everyone,
I have a very simple question....and I have been working on it for some time but cannot figure it out. This is essentially what I would LIKE to say:
for r = 1:length(FreqSec)-1
if FreqSec(1,r+1) > FreqSec(r)*1.01 "OR" FreqSec(1,r+1) <FreqSec(r)*0.99
LagStart = [FreqSec(1,r) r];
break;
end
end
FreqSec is a vector with lots and lots of values....generally within the range of 0.99 and 1.01, except for in a certain interval. I want to detect the exact index point at which the values start changing from the 0.99 to 1.01 range.
Thanks for the help in advance :)

  1 Comment

The "||" counts as an or on matlab

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2 Answers

Answer by Walter Roberson
on 3 Feb 2012
 Accepted Answer

if FreqSec(1,r+1) > FreqSec(r)*1.01 | FreqSec(1,r+1) <FreqSec(r)*0.99
or
if FreqSec(1,r+1) > FreqSec(r)*1.01 || FreqSec(1,r+1) <FreqSec(r)*0.99
The first of these is more general. The second of these, , is the short-circuiting OR that does not bother to evaluate the second expression if it already knows the final result after the first operation. The operator can only be used between expressions that produce scalar outputs.

  1 Comment

good clarification on the difference between | and !

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Answer by Geoff
on 3 Feb 2012

So you want the last index within the valid range?
I don't know why you are multiplying by 1.01 and 0.99. Perhaps you have described the problem incorrectly or that is the cause of your difficulties. What I think you are trying to do is this:
idx = find( FreqSec >= 0.99 & FreqSec <= 1.01, 1, 'last' )
LagStart = [FreqSec(1,idx) idx];
Or, since it's symmetric:
idx = find( abs(FreqSec-1) <= 0.01, 1, 'last' )
If instead you want the index of the first out-of-range value, use:
idx = find( abs(FreqSec-1) > 0.01, 1, 'first' )
The parameter 'first' is optional, but good for clarity.
-g-

  1 Comment

Geoff
on 3 Feb 2012
Oops, those statements with 'last' are incorrect. You are probably better off doing the 'first' statement and subtracting 1.

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