for loops and if else for matrices

Question

David Phung 2014-11-2

1
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https://ww2.mathworks.cn/matlabcentral/answers/161061-for-loops-and-if-else-for-matrices

评论： David Phung 2014-11-3

My homework question says that theres a file called pipe.dat with a matrix inside [4.64 15.30; 5.21 15.36; 4.79 15.39]. The weight is supposed to be between 4.5 and 5.1, inclusive, and the length is supposed to be between 15.3 and 15.4, inclusive. I'm supposed to write a script that will count how many 'rejects' there are. A reject is any piece of pipe that has an invalid weight and/or length.

Here is my code:

load pipe.dat
temp1=0;
pipe
for i=1:3
    if pipe(i,1)>=4.5 && pipe (i,1) <= 5.1 || pipe(i,2) >= 15.3 && pipe(i,2)<=15.4
        x=0;
          else 
              x=1;
              newnum=temp1+x;
      end
  end
  x

I'm not really sure how to tackle this problem. I've had a couple ideas, such as a nested if else statement.

load pipe.dat
temp1=0;
for i=1:3
    if pipe(i,1)>=4.5 && pipe (i,1) <= 5.1 
        x=0;
        if pipe(i,2) >= 15.3 && pipe(i,2)<=15.4
            x=0;
        else 
            x=1;
        end
    end
end
x

But Im not sure how to tackle this problem.

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Answer 1

Geoff Hayes 2014-11-2

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David - you won't need a nested if statement, just an if and an elseif - the first to to check to see if the pipe weight is invalid, and the second to check if the pipe length is invalid. If either condition is true, then you would increment your number of rejects counter.

 load pipe.mat;
 numRejects = 0;
 for k=1:size(pipe,1)
     % check the weight
     if pipe(k,1)<4.5 || pipe(k,1)>5.1
         numRejects = numRejects + 1;
     % check the length
     elseif pipe(k,2)<15.3 || pipe(k,2)>15.4
         numRejects = numRejects + 1;
     end
 end