solving four equations to find I1, I2, I3, I4 as functions of R1, R2, R3, V1 and V2

I have these four equations

• 9*I1 – 2*I3 + V1 + 4 = 0
• (5 + R3)*I2 – 5*I4 – 1 = 0
• -2*I1 + (2 + R1 + R2)*I3 - R1*I4 + 5 = 0
• -5*I2 - R1*I3 + (R1 + 15)*I4 + V2 = 0

I used the following code to find I1, I2, I3, I4 as functions of R1, R2, R3, V1 and V2

syms I1 I2 I3 I4
eqn1 = 9*I1 – 2*I3 + V1 + 4 == 0
eqn2 = (5 + R3)*I2 – 5*I4 – 1 == 0
eqn3 = -2*I1 + (2 + R1 + R2)*I3 - R1*I4 + 5 == 0
eqn4 = -5*I2 - R1*I3 + (R1 + 15)*I4 + V2 == 0
sol = solve([eqn1, eqn2, eqn3, eqn4], [I1, I2, I3, I4]);

However, I encountered the following error:

eqn1 = 9*I1 – 2*I3 + V1 + 4 == 0

↑

Error: Invalid text character. Check for unsupported symbol, invisible character, or pasting of non-ASCII characters.

how can I find I1, I2, I3, I4 as functions of R1, R2, R3, V1 and V2

Answer 1

[Sulaymon Eshkabilov]

Here is the corrected code (there were some character problmes and undeclared V1 V2 R1 R2 R3 vars):

syms I1 I2 I3 I4 V1 V2 R1 R2 R3
eqn1 = 9*I1 - 2*I3 + V1 + 4 == 0

eqn1 = 

eqn2 = (5 + R3)*I2 -5*I4 - 1 == 0

eqn2 = 

eqn3 = -2*I1 + (2 + R1 + R2)*I3 - R1*I4 + 5 == 0

eqn3 = 

eqn4 = -5*I2 - R1*I3 + (R1 + 15)*I4 + V2 == 0

eqn4 = 

sol = solve([eqn1, eqn2, eqn3, eqn4], [I1, I2, I3, I4]);
% See the solutions
SOLUTIONS = [sol.I1; sol.I2; sol.I3; sol.I4]

SOLUTIONS = 

[Moussa]

Thank you

if I want to find should I write 2*(sol.I1-sol.I2)^2 in Command Window?

[Torsten]

Yes, or

2*(SOLUTIONS(1)-SOLUTIONS(2)^2