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Set up an OR argument for equation

Asked by Grant Murdoch on 18 Mar 2019
Latest activity Answered by Jos (10584)
on 18 Mar 2019
I am using Matlab to simulate the pounding bwtween structures during earthquake events.
To do this the equation for the pounding force, F, must change depending on the output of another parameter. The conditions are:
F(t) = k*s + c*v(t) when v(t) > 0
F(t) = k*s when v(t) < 0
What is the best way to set this up?
The code for both the equations above is:
fp = (k_inp*(x1-x2-gap)+c_inp*(xdot_1-xdot_2)).*(sign(x1-x2-gap)+1)/2 when v(t) > 0
fp = (k_inp*(x1-x2-gap) when v(t) < 0
where v(t) = (xdot_1-xdot_2)).*(sign(x1-x2-gap)+1)/2
Thanks in advance for any replies.

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3 Answers

Answer by Torsten
on 18 Mar 2019
Edited by Torsten
on 18 Mar 2019
 Accepted Answer

v = (xdot_1-xdot_2)).*(sign(x1-x2-gap)+1)/2;
if v > 0
fp = (k_inp*(x1-x2-gap)+c_inp*(xdot_1-xdot_2)).*(sign(x1-x2-gap)+1)/2
else
fp = k_inp*(x1-x2-gap)
end

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Answer by Jos (10584)
on 18 Mar 2019

Can't you use logical indexing? A simplified example
v = 10:20
q = v > 13 & v < 18
f(q) = 2*v(q)
f(~q) = 30 + v(q)

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Answer by Jos (10584)
on 18 Mar 2019

Simpler, without an if-else:
v = (xdot_1-xdot_2)).*(sign(x1-x2-gap)+1)/2;
fp = (k_inp*(x1-x2-gap) + (v>0) * c_inp * (xdot_1-xdot_2)).*(sign(x1-x2-gap)+1)/2
% |||||||

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