How do I force a zero value in Simscape language
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I have the following equation inside my custom Simscape block.
Mloc == sqrt( (Pratio^(gm1/-A.gam) * (1+(gm1/2)*Minf^2) - 1) * (2/gm1) );
I am encountering an issue where Pratio is near 1.0 and Minf is near zero, however rounding errors are causing the value inside the sqrt to become negative. How do I force the value inside the sqrt to remain non-negative? Here are some example numbers showing this situation.
sqrt(((14.715780533017/14.715780064774)^(0.4/-1.4) * (1+(0.4/2)*0.0001079^2) - 1) * (2/0.4))
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Sebastian Castro
2016-3-25
I would start off by changing the equations to something like
let
X = (Pratio^(gm1/-A.gam) * (1+(gm1/2)*Minf^2) - 1) * (2/gm1);
in
if X >= 0
Mloc == sqrt(X);
else
Mloc == {0,'appropriate_unit'};
end
end
In reality, most Simscape language blocks will have some sort of "smoothing" to prevent the sharp discontinuity -- usually a linear ramp down to zero over some threshold range (see, e.g., the Translational/Rotational friction blocks). You can try that further step if you run into problems, though.
- Sebastian
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