# Solve a group of Symbolic Equations

4 views (last 30 days)
Matthew Worker on 25 Feb 2023
Edited: Dyuman Joshi on 25 Feb 2023
syms A B alpha beta % variable
syms R1 R2 C1 C2 % constant
eqn1 = A + B == 1/(R1*C1)
eqn1 =
eqn2 = -A*beta-B*alpha == 0
eqn2 =
eqn3 = alpha*beta == 1/(R1*C1*R2*C2)
eqn3 =
eqn4 = (R1*C1+R1*C2+R2*C2)/(R1*C1*R2*C2) == -alpha-beta
eqn4 =
[A,B,alpha,beta] = solve(eqn1,eqn2,eqn3,eqn4)
A =
B =
alpha =
beta =
A1 = simplify(A)
A1 =
B1 = simplify(B)
B1 =
alpha1 = simplify(alpha)
alpha1 =
beta1 = simplify(beta)
beta1 =
I want to get A1,B1,alpha1,beta1 represented only by constant (R1 R2 C1 C2). However, when I run the codes, the system gives me:
A1 =
1/(C1*(A + B))
1/(C1*(A + B))
B1 =
-(A^2*C1 + B^2*C1 - A*(C1*(A^2*C1 + B^2*C1 + 2*A*B*C1 + 4*A*B*C2))^(1/2) + B*(C1*(A^2*C1 + B^2*C1 + 2*A*B*C1 + 4*A*B*C2))^(1/2) + 2*A*B*C2)/(2*A*B*C1*C2*(A + B))
-(A^2*C1 + B^2*C1 + A*(C1*(A^2*C1 + B^2*C1 + 2*A*B*C1 + 4*A*B*C2))^(1/2) - B*(C1*(A^2*C1 + B^2*C1 + 2*A*B*C1 + 4*A*B*C2))^(1/2) + 2*A*B*C2)/(2*A*B*C1*C2*(A + B))
alpha1 =
((A + B)*((C1*(A^2*C1 + B^2*C1 + 2*A*B*C1 + 4*A*B*C2))^(1/2) + A*C1 - B*C1))/(2*B*(C1 + C2))
-((A + B)*((C1*(A^2*C1 + B^2*C1 + 2*A*B*C1 + 4*A*B*C2))^(1/2) - A*C1 + B*C1))/(2*B*(C1 + C2))
beta1 =
-((A + B)*((C1*(A^2*C1 + B^2*C1 + 2*A*B*C1 + 4*A*B*C2))^(1/2) + A*C1 - B*C1))/(2*A*(C1 + C2))
((A + B)*((C1*(A^2*C1 + B^2*C1 + 2*A*B*C1 + 4*A*B*C2))^(1/2) - A*C1 + B*C1))/(2*A*(C1 + C2))
What other codes should I add to solve this problem?

Dyuman Joshi on 25 Feb 2023
Edited: Dyuman Joshi on 25 Feb 2023
You need to specify which variables are you solving for -
syms A B alpha beta % variable
syms R1 R2 C1 C2 % constant
eqn1 = A + B == 1/(R1*C1);
eqn2 = -A*beta-B*alpha == 0;
eqn3 = alpha*beta == 1/(R1*C1*R2*C2);
eqn4 = (R1*C1+R1*C2+R2*C2)/(R1*C1*R2*C2) == -alpha-beta;
[A0,B0,alpha0,beta0] = solve([eqn1,eqn2,eqn3,eqn4],[A, B, alpha, beta]);
A0
A0 =
B0
B0 =
alpha0
alpha0 =
beta0
beta0 =

Walter Roberson on 25 Feb 2023
You have four equations in 8 unknowns. When you call solve() you should specify the names of the variables to solve for. solve() is not able to read the names of the variables you are assigning to in order to figure out which variables you want to solve for.

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