If statement with many logical or.

This is my code. I have a1 = 0.4 and b1 =0.2 and 1-a1-b1 = 0.4. Middle condition of if statement is satisfied but still it doesn't work. please help.

    % code
  for a1 = 0.4 : 0.1 : 1
    for b1 = 0.2 : 0.1 : 1
        if (a1 == b1 && b1 > 1-a1-b1) || (1-a1-b1 == a1 && a1 > b1) || (1-a1-b1 == b1 && b1 > a1)
           continue;
        end
        file_name = sprintf('file_%.2f_%.2f_%.2f.txt',a1,b1,1-a1-b1);
        fileID = fopen(file_name, 'w+');
        fclose(fileID);
    end
 end

[Kevin Chng]

if didt meet the middle condition, i guess you want to break the for loop (for b1=0.2:0.1:1).

 % code
  for a1 = 0.4 : 0.1 : 1
    for b1 = 0.2 : 0.1 : 1
        if (a1 == b1 && b1 > 1-a1-b1) || (1-a1-b1 == a1 && a1 > b1) || (1-a1-b1 == b1 && b1 > a1)
           continue;
        else
            break;
        end
        file_name = sprintf('file_%.2f_%.2f_%.2f.txt',a1,b1,1-a1-b1);
        fileID = fopen(file_name, 'w+');
        fclose(fileID);
    end
   end

Does it work for you?

[sourabh mittal]

No, it doesn't work. i want to skip for that particular value of a1 and b1, and go for next iteration if conditions of 'if' statement are satisfied.

[Kevin Chng]

How about this?

% code
  for a1 = 0.4 : 0.1 : 1
    for b1 = 0.2 : 0.1 : 1
        if (a1 == b1 && b1 > 1-a1-b1) || (1-a1-b1 == a1 && a1 > b1) || (1-a1-b1 == b1 && b1 > a1)
           break;
        end
        file_name = sprintf('file_%.2f_%.2f_%.2f.txt',a1,b1,1-a1-b1);
        fileID = fopen(file_name, 'w+');
        fclose(fileID);
    end
   end

[madhan ravi]

Can you explain what you want to obtain ?

[Adam]

Which next iteration do you want to go to? If you want to go to the next iteration of the inner loop than 'continue' works fine if your logical statement is correct to catch the case you want. If you want to skip to the next iteration of the outer loop then 'break' is required.

So what is the actual problem you are having? Is the logical statement correct, but the behaviour when it matches that is not what you want or is it not continuing when you expect because the logical statement is not correct?

[sourabh mittal]

no it still doesn't work. I guess problem is in comparing flot values.

[sourabh mittal]

I want to to go to the next iteration of the inner loop, so 'continue' works fine. but when a1 = 0.4 and b1 =0.2 , (middle condition of if is satisfied) i am still getting a file_0.4_0.2_0.4.

[Adam]

Yes, looking at the loop again, this could well cause a problem.

[sourabh mittal]

 % code
 for a1 = 0.4 : 0.1 : 1
    for b1 = 0.2 : 0.1 : 1
        if  (1-a1-b1 == a1 && a1 > b1) 
           continue;
        end
        file_name = sprintf('file_%.2f_%.2f_%.2f.txt',a1,b1,1-a1-b1);
        fileID = fopen(file_name, 'w+');
        fclose(fileID);
    end
 end

See this condition of if statement. this is not working as i described above.

Answer 1

[Dennis]

You are comparing floating point numbers, which will not necessary work:

1-0.4-0.2==0.4

ans =

       0

You can use

abs(1-a1-b1-a1)<0.001

For more information please look here.

Answer 2

[John D'Errico]

Your problem is EXACTLY in that you are trying to compare floating point numbers, for exact equality. This is something you should never do, unless you completely understand floating point numbers, and how to know when you can do it safely. And even then you still need to take extra care.

But tests like this:

b1 > 1-a1-b1

are just a flat out bad idea. NEVER DO THAT. NEVER. Must I say it again? Don't do it. Period. For example, just how does 0.4 compare to 1-0.2-0.4? Surely they are the same number?

sprintf('%0.55f',0.4)
ans =
    '0.4000000000000000222044604925031308084726333618164062500'

sprintf('%0.55f',1 - 0.4 - 0.2)
ans =
    '0.3999999999999999666933092612453037872910499572753906250'

Not so.

Instead, you do have options.

for a1i = 4 : 10
  a1 = a1i/10;
  for b1i = 2 : 10
    b1 = b1i/10;
    if (a1i == b1i && b1i > 10-a1i-b1i) || (10-a1i-b1i == a1i && a1i > b1i) || (10-a1i-b1i == b1i && b1i > a1i)

yada yada yada...

As you should see, I changed all of your numbers to be integers, double precision integers, but still integers. All of the tests (assuming I did not mistype anything in that last line) work on INTEGERS, thus are comparisons between integers.

Compute a1 and b1 separately. Use them in floating point form, but NEVER use them for comparisons. NEVER. Well, again, unless you seriously know what you are doing, and you know why you should never use tests of that form.

Answer 3

[ANKUR KUMAR]

Write statement inside of the loop

for a1 = 0.4 : 0.1 : 1
    for b1 = 0.2 : 0.1 : 1
        if (a1 == b1 && b1 > 1-a1-b1) || (1-a1-b1 == a1 && a1 > b1) || (1-a1-b1 == b1 && b1 > a1)
            file_name = sprintf('file_%.2f_%.2f_%.2f.txt',a1,b1,1-a1-b1);
            fileID = fopen(file_name, 'w+');
            fclose(fileID);
        end
    end
end