Why my matlab does not enter a loop even when the conditions are true

clear all
Amp=35;
freq=2.3;
for i=1:5
    for j=1:4
        if Amp== 35 && freq==2.3
            robot_speed = 1
        end
        if Amp== 40 && freq==2.3            
            robot_speed = 2
        end
        if Amp== 35 && freq==2.7
            robot_speed = 6
        end
        if Amp== 40 && freq==2.7
            robot_speed = 7
        end
       if Amp== 35 && freq==3.1
            robot_speed = 11
        end
        if Amp== 40 && freq==3.1
            robot_speed = 12
        end
        if Amp== 35 && freq==3.5
            robot_speed = 16
        end
        if Amp== 40 && freq==3.5
            robot_speed = 17
        end
        freq=freq+0.4;
    end
    freq=2.3;   
    Amp=Amp+5;
end
Here when the value of Amp becomes equal to 35 and freq becomes equal to 2.7, the robot_speed should be equal to 6 but when I run the code, Matlab is unable to enter the loop even when condition suffices. Loop is traversed only for :

if Amp== 35 && freq==2.3
            robot_speed = 1
end
if Amp== 40 && freq==2.3            
            robot_speed = 2
end

Why is this happening? Someone please help me.

Answer 1

[Walter Roberson]

MATLAB works in binary not in decimal. The only freq value in your code that can be exactly represented in binary is 3.5

Do not compare floating point numbers for exact equality. Consider using ismembertol. Or consider using integers representing tenths and divide them by 10 only when needed in a calculation

Answer 2

[Guillaume]

Note, rather than an endless list of if statements, you should be using the power of computers who can do look ups very easily:

lookuptable = [35 2.3 1      %Amp, frequency, resulting speed 
               40 2.3 2
               35 2.7 6
               40 2.7 7
               35 3.1 11
               40 3.1 12
               35 3.5 16
               40 3.5 17];  
Amp = 35;
freq = 2.3;

for i = 1:5
    for j = 1:4
       [matched, matchedrow] = ismembertol([Amp, freq], lookuptable(:, [1 2]), 'ByRows', true);
       if matched
          robot_speed = lookuptable(matchedrow, 3);
       end
       freq = freq + 0.4;
    end
    freq = 2.3;   
    Amp = Amp + 5;
end

Isn't this simpler (and a lot less typing)?

[Stephen23]

+1 and more aesthetically pleasing.

Answer 3

[Aditi]

Thank you for your suggestion. Instead of using my earlier approach, I implemented all the loops as:

if abs(Amp-35) <= 0.001 && abs(freq-2.3) <= 0.001
            robot_speed = 1
end