Q = 
Substitute partial differential into symfun
显示 更早的评论
Because my actual functions are very complex, I would like to calculate the derivative of nested functions first and then substitute the functions afterwards.
A minimal example looks like this:
syms G(h) h(t) t
Q = G(h)
dGdt = diff(Q,t) % -> D(G)(h(t)) occurs
% Now define G(h) and derive:
G = h^2;
dGdh = diff(G,h)
How is it possible, to insert the derivative of G with respect to h as the partial derivative?
I tried this, but it is not working:
% dQ_subs = subs(dGdt, D(G), dGdh)
% dQ_subs = subs(dGdt, D(G)(h(t)), dGdh)
I really appreciate any feedback!
采纳的回答
syms G(h) h(t) t
Q = G(h)
dGdt = diff(Q,t) % -> D(G)(h(t)) occurs
s = children(dGdt)
% Now define G(h) and derive:
G = h^2;
dGdh = diff(G,h)
subs(dGdt,s{1},dGdh)
2 个评论
Hi Torsten,
I think it works easier, and perhaps more generally, to define G as a function of its own dummy variable.
syms G(x) h(t) t
Q = G(h);
dGdt = diff(Q,t) % -> D(G)(h(t)) occurs
% Now define G(x) and derive:
G(x) = x^2;
subs(dGdt)
Slightly more complicated case
G(x) = x^2 + sin(x);
subs(dGdt)
ludolfusexe
2024-5-16
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