Symbolic Derivative in matlab

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HN 2020-8-17

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https://ww2.mathworks.cn/matlabcentral/answers/580803-symbolic-derivative-in-matlab

编辑： HN 2020-8-18

采纳的回答： KSSV

Can matlab diffrentiate F with respect to θ , ϕ and ψ only ?.

Any help is apperciated

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采纳的回答

KSSV 2020-8-17

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https://ww2.mathworks.cn/matlabcentral/answers/580803-symbolic-derivative-in-matlab#answer_481281

You can carry on symbolic calculations. Read about diff.

https://www.mathworks.com/help/symbolic/diff.html

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KSSV 2020-8-18

在 MATLAB Online 中打开

syms A B C t th 
R =   -A*(cos(t)-cos(t))+B*cos(th)*sin(t);
S =    A*sin(t)*sin(t)-B*cos(t)+C*cos(t);
phi=atan(R/S)

HN 2020-8-18

编辑：HN 2020-8-18

在 MATLAB Online 中打开

Why running on live script and script gives different result for the same expression?

syms syms t phi(t) theta(t) psi(t)  dphi dtheta dpsi  rp L alpha beta
x=rp*sin(alpha)*(cos(theta)*sin(phi) - cos(phi)*sin(psi)*sin(theta)) - rp*cos(alpha)*(cos(phi)*cos(theta) + sin(phi)*sin(psi)*sin(theta)) + (rp*cos(psi)*(sin(alpha + phi) - sin(phi)))/tan(alpha)
diff(x, t)

using matlab mlx and matlab script. Both gives different result

mlx gives

vx=rp*cos(psi(t))*cos(theta(t))*sin(phi(t))*sin(alpha) - rp*cos(phi(t))*cos(psi(t))*cos(theta(t))*cos(alpha)

while running on matlab script gives

vx=((rp*cos(psi(t))*(cos(alpha + phi(t)) - cos(phi(t)))*diff(phi(t), t))/tan(alpha) - rp*sin(alpha)*(sin(phi(t))*sin(theta(t))*diff(theta(t), t) - cos(phi(t))*cos(theta(t))*diff(phi(t), t) + cos(phi(t))*cos(psi(t))*sin(theta(t))*diff(psi(t), t) + cos(phi(t))*cos(theta(t))*sin(psi(t))*diff(theta(t), t) - sin(phi(t))*sin(psi(t))*sin(theta(t))*diff(phi(t), t)) - rp*cos(alpha)*(cos(phi(t))*sin(psi(t))*sin(theta(t))*diff(phi(t), t) - cos(phi(t))*sin(theta(t))*diff(theta(t), t) - cos(theta(t))*sin(phi(t))*diff(phi(t), t) + cos(psi(t))*sin(phi(t))*sin(theta(t))*diff(psi(t), t) + cos(theta(t))*sin(phi(t))*sin(psi(t))*diff(theta(t), t)) - (rp*sin(psi(t))*(sin(alpha + phi(t)) - sin(phi(t)))*diff(psi(t), t))/tan(alpha))

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