Limiting Precision on MATLAB
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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.
采纳的回答
David Fletcher
2018-2-26
1 个投票
Could try forceSum=int32(T-W)
更多回答（3 个）
James Tursa
2018-2-26
编辑：James Tursa
2018-2-26
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.
Walter Roberson
2018-2-26
1 个投票
"Any idea of making MATLAB read this value as 0?"
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