How to plug in one symbolic equation into another
15 views (last 30 days)
Show older comments
If I have a system of differential equations:
(1) d A(t) / dt = 2*A(t)
(2) d B(t) / dt = 3*B(t)
And now, I also have:
(3) C(t) = A(t) + (B(t)^2)
--> I tell Matlab to differentiate C(t):
d C(t) / dt = A'(t) + 2*B(t)*B'(t)
where A'(t) = d A(t) / dt, same for B'(t)
How do I tell Matlab to "plug in" for C'(t) using equations 1 and 2?
0 Comments
Accepted Answer
Aylin
on 27 Dec 2016
Edited: Aylin
on 27 Dec 2016
Hello,
The subs function can be used to "plug in" values for the C'(t) equation.
In this answer, I use the Symbolic Math toolbox syntax from MATLAB R2016b. If you are using a previous version of MATLAB, you may have to adjust the syntax before using this code.
To elaborate further on your example, if A, B, and C are defined as symbolic functions of t:
syms A(t) B(t) C(t)
and eqA, eqB, eqC, and eqDC are the defined symbolic equations:
eqA = diff(A) == 2*A
eqB = diff(B) == 3*B
eqC = C == A + (B*B)
eqDC = diff(eqC)
then the subs function can be used as follows to substitute eqA for dA/dt:
eqDC_subA = subs(eqDC, diff(A), eqA)
and can be used for eqB too:
eqDC_subA_subB = subs(eqDC_subA, diff(B), eqB)
Please refer to the Symbolic Math Toolbox documentation for the subs function for more information:
0 Comments
More Answers (0)
See Also
Categories
Find more on Calculus in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!