Ode45: constraining values of variables evolution

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Mohammad Farhat 2020-3-30

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https://ww2.mathworks.cn/matlabcentral/answers/514090-ode45-constraining-values-of-variables-evolution

回答： Walter Roberson 2020-3-30

How can I constrain the values of the integrated variables in ode45.

I found "opts = odeset('NonNegative',1)" can constrain the first solution component to be positive, I need a similar option but to constrain the values within a certain range or nature (example: I need x to be real and 3<x<4 ).

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Answer 1

Walter Roberson 2020-3-30

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https://ww2.mathworks.cn/matlabcentral/answers/514090-ode45-constraining-values-of-variables-evolution#answer_422954

See the ballode example for how to use Events to terminate ode integration and restart it with the new parameters.

The nonnegative option is only intended for system that might plausibly go negative due to rounding error or interpolation error; it is not intended to confine a system that would properly go negative to be non-negative.