# I need to solve a system of equations, without the syms command.

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Petch Anuwutthinawin on 29 Jul 2021
Edited: Cris LaPierre on 29 Jul 2021
%I have a system of equations based off of Kirchoff law (e1-e6) that are
%all simultaneously true. The code works to solve for i4 which is the
%answer needed, but I have to do it without the syms command.
syms i1 i2 i3 i4 i5 i6
e1=v-R2*i2-R4*i4==0; %given equations 1-6
e2=-R2*i2+R1*i1+R3*i3==0;
e3=-R4*i4-R3*i3+R5*i5==0;
e4=i6==i1+i2;
e5=i2+i3==i4;
e6=i1==i3+i5;
eqns=[e1,e2,e3,e4,e5,e6];
vars=[i1 i2 i3 i4 i5 i6];
[A,b] = equationsToMatrix(eqns,vars);
X=double(A\b);
i4=X(4)
%How do I change this code so I can do it without the syms command?

Cris LaPierre on 29 Jul 2021
Set up your system of linear equations and solve using left divide.
Cris LaPierre on 29 Jul 2021
Sorry, I was thinking of using current loops. You can use nodes, too. You already have your equations. Just write them in matrix form. x contains the currents (i1-i6), A contains the value to multiply current by, and b contains the resulting value. Just keep track of how you multiply matrices (march across the row of A, and down the columns of x).
For example, you have the equation v-R2*i2-R4*i4==0. I'd rearrange this to be R2*i2+R4*i4=v. In matrix form, this is To add one of your current equations, use 1s and 0s to create the math. For example, to add this equation: i6=i1+i2 to the matrix, I would rearrange it to be i1+i2-i6=0. In matrix form, that looks like this: You have 6 unknowns, so you need six equations. Convert your remaining equations to matrix form, and then solve using left division.