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Symbolic matlab: how to set a variable as a function of time?

조회 수: 189(최근 30일)
Sebastian D'Amico
Sebastian D'Amico 2012년 2월 15일
댓글: Sergei Sergienko 2020년 6월 13일
Hello to all! I'm trying to set a symbolic variable as a function of "t". This is because I need to obtain something like this:
K>> diff(sin(theta),t)
ans = diff(theta,t)*cos(theta)
or
ans= theta_dot*cos(theta)
but how to tell Matlab that variable theta is a function of time "t"?
Thank you!
  댓글 수: 1
Ezequiel Garcia
Ezequiel Garcia 2017년 4월 18일
You need to declare t as a "symbolic"
syms t;

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답변(4개)

Walter Roberson
Walter Roberson 2012년 2월 15일
syms theta t
diff(sin(theta(t)),t)
  댓글 수: 2
Sergei Sergienko
Sergei Sergienko 2020년 6월 13일
Is it possible to make vector function of t? Something like this
sym('q(t)', [3 1])
diff(sin(q),t)

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Wayne King
Wayne King 2012년 2월 15일
Hi Sebastian, do you know the expression for theta(t)?
syms theta t;
theta(t) = t^2;
diff(cos(theta),t)

Sebastian D'Amico
Sebastian D'Amico 2012년 2월 15일
Wayne, thank you for your answer! I don't have the expression of theta because I don't need it. This is the reason I need to tell Matlab that theta is a function of "t" so, when derivate is computed, it should consider that, for example, diff(sin(theta),t) is equal to diff(theta,t)*cos(theta). But, how to set it?
Seabstian
  댓글 수: 1
Wayne King
Wayne King 2012년 2월 15일
Do you really need that if you do not know the expression for theta(t), you know df(theta)/dt = df/dtheta*dtheta/dt

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sharara rehimi
sharara rehimi 2018년 8월 16일
thanks a lot..great for my problem

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