Why does .gt return a vector for simple comparison of two numbers?

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Don
Don 2015-10-15
评论： Walter Roberson 2015-10-16
The problem: Trying to count heart rate. I have a (somewhat noisy) signal vector of length 30K or so and intend to analyze peak-to-peak times using the nearest-neighbor approach described in the tutorial
Heartrate (BPM) Example Matlab Code | dadorran https://dadorran.wordpress.com/2014/05/22/heartrate-bpm-example-matlab-code/
This approach reads the data into sig(k), establishes a “cutoff” value, searches for peaks that are greater than the two nearest neighbors AND exceed a cutoff threshold.
Example data:
sig(6)= 385.9312
sig(7) = 406.9276
sig(8) = 257.9995
cutoff = 600
WHY does this occur??
sig(7)>cutoff
ans = 1 1 1
Here’s the code:
j=1;
PtoP=[];
beat_count = 0;
for k = 2:length(sig)-1
if sig(k)>cutoff;
if(sig(k)>sig(k-1));
if(sig(k)>sig(k+1));
beat_count=beat_count+1;
PtoP(j)=k;
j=j+1;
end;
end;
end;
end;
MANY THANKS for any help here

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采纳的回答

Don
Don 2015-10-16
I don't think I am dealing with 3-element vectors k
k =
31231
>> sig(k)
ans =
-263.9811
>> cutoff
cutoff =
600
>> beat_count
beat_count =
3288
>> sig(k)>cutoff
ans =
0 0 0
  2 个评论
Don
Don 2015-10-16
k
k =
31231
>> sig(k)
ans =
-263.9811
>> cutoff
cutoff =
600
>> beat_count
beat_count =
3288
>> sig(k)>cutoff
ans =
0 0 0
Guillaume
Guillaume 2015-10-16
One possibility is that you've shadowed the comparison operator with a local function or variable. What does
which gt
return ?

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更多回答（2 个）

Steven Lord
Steven Lord 2015-10-16
I predict that if you check the class of the variable cutoff, it is of class char not a numeric class.
c = '600'
c will be displayed as 600, but it is in fact a vector of 3 characters, '6', '0', and '0'. When you convert cutoff into a number using STR2NUM or similar, you should receive a scalar result from sig(k)>cutoff.
  1 个评论
Walter Roberson
Walter Roberson 2015-10-16
Good catch, Steven. The spacing of the result supports that hypothesis. If the 600 had been numeric there would have been spaces before the digits.

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Walter Roberson
Walter Roberson 2015-10-16
If you have
sig(7)>cutoff
returning a vector of 3 values, then your cutoff must have become a vector of 3 values.
And if
sig(k)>cutoff
returns a vector of 3 values, then either your cutoff has become a vector of 3 values or else your k has become a vector of 3 values.

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