Extra term in "min" function in while loop

Question

Adam 2014-5-27

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评论： Adam 2014-5-27

I was given a piece of code to work on and edit but I'm running into a few errors because I am unsure what this extra piece of term means in the code, the code looks like this:

while DC1(1,j) ~= min(DC1(:,450:Xep)),DC1(1,j);
   Xbp = j;                    
   j=j+1;
end

I can understand the fact that DC1 is searching for the position of the minimum value term in itself by comparing it using the "min" function. What I do not understand is why there is that extra

",DC1(1,j)" bit. Do you know what it is? Thanks.

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Answer 1

Roger Wohlwend 2014-5-27

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The min function compares the vector DC1(:,450:Xep) to the scalar DC1(1,j). The result is a vector that is identical to DC1(:,450:Xep) except that all values that are greater than DC1(1,j) are replaced by DC1(1,j). Then this vector is compared to DC(1,j).

If Xep > 451 then DC1(:,450:Xep) is a vector and as I just wrote the result of the min function is a vector. When you compare a scalar to a vector you get a vector of logical values, but to control a loop you should not use a vector of logicals but only one single logical. If you provide a vector, I'm not completely sure, what Matlab does. I would avoid it because you risk that the code does not always do what it should. Perhaps the guy who wrote the code meant something like this:

while DC(1,j) ~= min(DC1(:,450:Xep))

That would make more sense.

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Adam 2014-5-27

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well originally when I found the code it was simply on the next line like this:

while DC1(1,j) ~= min(DC1(:,450:Xep))

,DC1(1,j);

But because of that "," i figured he ment to leave it on the first line but took it down for keeping the code clean or prevent lines from getting to long.

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