Solving multiple equations to derive transfer function

[Valyence]

I am trying to solve a system of equations that i derived from nodal analysis of a circuit but i am having trouble figuring out how to get mathcad to symbolicly solve the system. If someone could tell me what i am doing wrong it would be great.

Thanks.

[RichardJ]

You have three equations and two unknowns. You need the same number of equations as unknowns.

[MikeArmstrong · Accepted solution]

Solution found see attached, but not sure on the validity of the results.

Mike

[RichardJ]

Solution found see attached

A solution. Pick two different equations, and you will get a different solution because the equations are not consistent.

but not sure on the validity of the results.

If the solution is valid then the third equaton isn't

[Valyence]

Yes thank you I added one extra node in my analysis that i didn't need thank you for the Help!

[MikeArmstrong]

Just out of curiosity, way are you choosing to solve it symbolically? Have you values for A, B, C, R, and S?

Mike

[Valyence]

It is for a lab that we are required to solve it symbolically and then given a notch frequency find the different values of R and C. Where A and B are two node voltages and I = input, O=output

[MikeArmstrong]

It is for a lab that we are required to solve it symbolically and then given a notch frequency find the different values of R and C. Where A and B are two node voltages and I = input, O=output

Right I get it.

You should have told me to mind my own business.

Mike

[Valyence]

HaHa..No worries i appreciate the help.

[LouP]

In your original post, the last term in the first equation is nonlinear in the node voltages, with the expression (A-I)*I. Is this an error? If it's a linear circuit (R,L and C only), then this type of term should not appear.

With 3 equations and 4 unknown voltages (A,B, I,O), I assume you want a solution of the form O=(fct of R's and C's)*I, with A and B eliminated. If the first equation is in fact linear, then there should be a way to set up the equations to get a symbolic solution.

Lou

[RichardJ]

I should have said, "in general not consistent". There are specific values of A, B, C, R, and S that could be chosen to make it consistent, but that would then be the solution for the third unknown

[MikeArmstrong]

A solution. Pick two different equations, and you will get a different solution because the equations are not consistent.

I don't understand what your getting at here. He gave three equations but only needed two in order to find O & I.

If the solution is valid then the third equaton isn't

Or the first equation isn't

It seems Matthew got his answer

Mike

[RichardJ]

I don't understand what your getting at here. He gave three equations but only needed two in order to find O & I.

Which two? If you solve only for O and I there are three possible solutions, depending on which pair of equations you choose. The three solutons are, in general, different.

They could be the same if the values of A, B, C, R, S satisfy a specific relationship, but then you are really solving for O, I and one more variable (take your pick).