Limiting Precision on MATLAB

I have a condition for a switch statement. For example:

% Program variables and input prompts
runProgram = 1;
i = 1;
prompt_massRatio = 'Enter m/M Ratio: ';
prompt_Us = 'Enter Static friction: ';
prompt_Uk = 'Enter kinetic friction: ';
prompt_theta = 'Enter block angle: ';

% Graph variables F vs. m/M
Fplot = [];
massFraction = [];

% Program start
while runProgram == 1

    % Calculation Variables
    m_M = input(prompt_massRatio);
    angle = input(prompt_theta);
    theta = angle*(pi/180);
    Us = input(prompt_Us);
    Uk = input(prompt_Uk);
    g = 9.81;
    T = m_M*g;
    W = g*sin(theta);
    Fs = cos(theta)*g*Us;
    Fk = cos(theta)*g*Uk;

      % Conditions
      forceSum = T - W;
      switch (true)
        case (forceSum < 0)

In this case, when forceSum is calculated for the conditions of m_M = 0.5, angle = 30, we get a value that is essentially zero but MATLAB does not read it as zero for the case statement. I.E. forceSum returns 8.8818e-016.

Any idea of making MATLAB read this value as 0?

Thanks for any help.

Answer 1

[David Fletcher]

Could try forceSum=int32(T-W)

Answer 2

[James Tursa]

With floating point calculations you often need to use tolerances, so this

if( forceSum < 0 )

would be coded something like this instead

if( abs(forceSum) < tol )  % for some appropriate tolerance

So all of your conditional tests should probably be modified into some type of tolerance test.

Answer 3

[Walter Roberson]

"Any idea of making MATLAB read this value as 0?"

See https://www.mathworks.com/matlabcentral/answers/47142-how-to-set-matlab-precision-to-single#comment_97018

Answer 4

[Robert Dominski]

Thanks for the help and links. It worked.

Cheers! You guys are great.