Problem with if function and decimal numers

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

Answer 1

[Image Analyst]

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

[Nicola]

You rock man! Thanks so much!

Answer 2

[Amit]

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.

[Nicola]

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