Hej, me and my study group have an issue regarding substituting time derivative of a variable with some more convinient expression.

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eqn = ............... + diff(x(t), t) + a*b*c...................;
So in the above equation there is a variabel named diff(x(t), t), this variable was introduced earlier in the script.
Now we want to substitute it with another more convinient name such as:
syms x_dot;
subs(eqn, 'diff(x(t), t)', x_dot);
But this gives a long list of errors, does anybody know why this is so difficult?
It is no problem to achieve when we substitute another variable from eqn such as:
syms x_dot;
subs(eqn, a, x_dot);

采纳的回答

Ameer Hamza
Ameer Hamza 2020-10-1
Don't input the symbolic expression as string. Following works
syms y(x) dy
eq1 = diff(y)^2
subs(eq1, diff(y, x), dy)

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