How to substitute a value for the time derivative of a function

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Hazim Nasir 2018-12-17

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评论： madhan ravi 2018-12-17

采纳的回答： madhan ravi

Hellow

I have a dispalcemet function of time defined as:

syms d(t)

>> a = d^2+sin(d)

The first derivative is the velocity:

>> v = diff(a)

v(t) =

cos(d(t))*diff(d(t), t) + 2*d(t)*diff(d(t), t)

the parameter diff(d(t), t) means the velocity value but How I can substitute a value for it using subs or any other function?

thank you

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采纳的回答

madhan ravi 2018-12-17

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https://ww2.mathworks.cn/matlabcentral/answers/436186-how-to-substitute-a-value-for-the-time-derivative-of-a-function#answer_352813

编辑：madhan ravi 2018-12-17

在 MATLAB Online 中打开

use subs() like below:

syms d(t)
a = d^2+sin(d);
v = diff(a);
after=subs(v,diff(d),2)  % here diff(d) is replace number 2

Gives:

after(t) =
 
2*cos(d(t)) + 4*d(t)

or use ode45() -> diff(d,2)==>acceleration the right hand side is as it is so we treat them now as second order ode which is then further reduced to first order odes.

[t,x]=ode45(@myod2,[0 2],[0;1]);
figure(1)
plot(t,x(:,1),'-ok')
figure(2)
plot(t,x(:,2),'-or')
function dxdt = myod2(t,Y) 
dxdt=[Y(2);
 sin(Y(1)) + Y(1)^2];
end