Solving Symbolic equations by solve command
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Hi I am trying to solve following system of symbolic equations but I do not know why I am not getting any result.
syms I1 I2 I3 I4 V1 V2 S
I would like to find V1/V2 meaning I like to find V2 based on V1 or vice versa. Can anyone tell me how to do that the final answer should not be dependent on I1, I2, I3 and I4 only to S.
Star Strider on 19 Jun 2015
I’m not quite sure what network you’re analysing. One problem is that while your first equation is correct in terms of the capacitive reactances 1/(s*C), the others are incorrect. Also, I don’t see any equations relating ‘I1’ or ‘I2’ in terms of ‘I3’ or ‘I4’. The systems seem to be unconnected.
It seems you are using node-voltage analysis. I would solve each branch as a current as a function of the voltages through it (KVL), then develop separate equations for the currents in terms of KCL, just as you would if you were calculating them by hand. Set your equations up for your branch currents (not difficult for systems of small equations), then let MATLAB solve your system from them.
Walter Roberson on 19 Jun 2015
Edited: Walter Roberson on 19 Jun 2015
You have 4 equations in 7 unknowns. You can eliminate I1, I2, I3, I4 by solving for those, but the result is going to be in V1, V2 and S. That does not give you enough information to relate V1 to V2 in terms of S. In order to do that you need two more equations: if you solve 6 equations in 7 unknowns then the results will be in terms of the 7th variable.
Note: when you have a set of equations, you need to solve them for as many variables as there are equations. You might not care what the values are of the other variables but you must supply their names to solve() so it knows what to isolate.