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

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

[Star Strider]

I can’t reproduce that. When I copy sig(6:8) to my workspace and execute:

sig(7)>cutoff

ans =
     0

Answer 1

[Don]

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

[Don]

 k

k =

       31231

>> sig(k)

ans =

 -263.9811

>> cutoff

cutoff =

600

>> beat_count

beat_count =

        3288

>> sig(k)>cutoff

ans =

     0     0     0

[Guillaume]

One possibility is that you've shadowed the comparison operator with a local function or variable. What does

which gt

return ?

Answer 2

[Steven Lord]

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.

[Walter Roberson]

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.

Answer 3

[Walter Roberson]

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.