Problem with if function and decimal numers

Question

Nicola 2014-1-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/112190-problem-with-if-function-and-decimal-numers

评论： Nicola 2014-1-13

Good evening, i have a problem with this code:

a=1:0.1:2;
b=0.1;
for i=1:1:10
    angoloutile(i)=a(i);
end
for j=1:1:10
    integ = fix(angoloutile(j)) ;
    fract = abs(angoloutile(j)- integ);
 if fract == b 
          angoloutile(j)=angoloutile(j)+0.5
      end
  end
for k=1:1:10
    angoloutile(k)
end

it doesn't take the IF function

if fract == b

but i'm sure that angoloutile(2) is 1.1 Thanks

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Answer 1

Image Analyst 2014-1-13

1
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The problem was using fix instead of rounding. Try this where I use int32() to cast to the nearest integer. I also cleaned up your if to make it more efficient and reduce the number of if tests by a factor of 10.

a=1:0.1:2;
for i=1:1:10
  angoloutile(i)=a(i);
end
for j=1:1:10
  integ = fix(angoloutile(j));
  fract = abs(angoloutile(j)- integ);
  fract=fract*10;
  deci=int32(fract);
  fprintf('j = %d, angoloutile(j) = %f, integ = %d, fact = %f, deci = %d\n', ...
    j, angoloutile(j), integ, fract, deci);
  if deci == 1
    angoloutile(j)=angoloutile(j)+0.5;
  elseif deci == 2
    angoloutile(j)=angoloutile(j)-0.08;
  elseif deci == 3
    angoloutile(j)=angoloutile(j)-0.12;
  elseif deci == 4
    angoloutile(j)=angoloutile(j)-0.16;
  elseif deci == 5
    angoloutile(j)=angoloutile(j)-0.20;
  elseif deci == 6
    angoloutile(j)=angoloutile(j)-0.24;
  elseif deci == 7
    angoloutile(j)=angoloutile(j)-0.28;
  elseif deci == 8
    angoloutile(j)=angoloutile(j)-0.32;
  elseif deci == 9
    angoloutile(j)=angoloutile(j)-0.36;
  end
end
% Print to command window.
angoloutile

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Nicola 2014-1-13

You rock man! Thanks so much!

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Answer 2

Amit 2014-1-13

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https://ww2.mathworks.cn/matlabcentral/answers/112190-problem-with-if-function-and-decimal-numers#answer_120689

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The issue is very small difference in floating point numbers, like 1.00000 and 1.0000000001. There is negligible difference however they are not equal. You can do something like:

tol = 1e-6;
if (fract-b) < tol

This will work.

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Nicola 2014-1-13

在 MATLAB Online 中打开

I'm sorry but your answer doesn't work for me. I changed the code and now is:

a=1:0.1:2;
for i=1:1:10
    angoloutile(i)=a(i);
end
for j=1:1:10
    integ = fix(angoloutile(j));
    fract = abs(angoloutile(j)- integ);
    fract=fract*10;
    deci=fix(fract);
      if deci == 1 
          angoloutile(j)=angoloutile(j)+0.5;
      end
      if deci == 2 
          angoloutile(j)=angoloutile(j)-0.08;
      end
      if deci == 3
          angoloutile(j)=angoloutile(j)-0.12;
      end
      if deci == 4 
          angoloutile(j)=angoloutile(j)-0.16;
      end
      if deci == 5 
          angoloutile(j)=angoloutile(j)-0.20;
      end
      if deci == 6
          angoloutile(j)=angoloutile(j)-0.24;
      end
      if deci == 7 
          angoloutile(j)=angoloutile(j)-0.28;
      end
      if deci == 8 
          angoloutile(j)=angoloutile(j)-0.32;
      end
      if deci == 9
          angoloutile(j)=angoloutile(j)-0.36;
      end
  end
for k=1:1:10
    angoloutile(k)
end

I need that if 1.0 nothing happens,if 1.1 it becomes 1.6, if 1.2 it becomes 1.12, if 1.3 it becomes 1.18 etc... The problem is that this trick doesn't work for 1.2!I don't know why it writes 1.7! and also 1,4 it writes 1,28 and not 1,24! Thanks so much

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