Solving composite equations with symbolic toolbox
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Nicholas Davis
on 1 Jun 2021
Commented: Sulaymon Eshkabilov
on 2 Jun 2021
Hi all,
I have a very simple code written to solve for two variables within two equations. My main variables are A and B, which are renamed to AR and BR later in the program. My constants are w, g, alphaL, and p. The initial equation is quadratic and thus will have two answers. I want each of these answers to be plugged into a new equation, a cubic equation, to therefore produce 6 differing solutions. I am not sure how to do this via symbolic toolbox, so any help would be seriously appreciated. Thanks!
syms A B w g alphaL p % w = (mu - V0)
eqn = B*(A + B)*(2*w - g*(A + 2*B)) - alphaL^2 == 0;
AR = solve(eqn,A);
neqn = -4*(B - p)*(AR + B - p)*(2*w - g*(AR + 2*B + p)) == 0;
BR = solve(neqn,B);
3 Comments
John D'Errico
on 1 Jun 2021
You CAN do it that way, at least, in this case, you can. However, the symbolic toolbox is better used to solve the two equations simultaneously. It has no problem with understanding there should be 6 solutions. @Sulaymon Eshkabilov shows how to do that.
Accepted Answer
Sulaymon Eshkabilov
on 1 Jun 2021
Hi,
Here is the corrected code with the symbolic solutions (A, B) of the two equations:
clearvars
syms A B w g alphaL p AR
eqn1 = B*(A + B)*(2*w - g*(A + 2*B)) - alphaL^2 == 0;
eqn2 = -4*(B - p)*(AR + B - p)*(2*w - g*(AR + 2*B + p)) == 0;
SOL = solve(eqn1, eqn2,A, B);
A_solution=SOL.A;
B_solution=SOL.B;
Good luck.
2 Comments
Sulaymon Eshkabilov
on 2 Jun 2021
Most welcome!
The last two lines are separation of solutions of A and B variables.
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