how to solve multi variable simultaneous equations

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Hedayat
Hedayat 2018-11-13
回答： Hedayat 2018-11-13
Hi all,
Please help me wiht this, I am new to matlab.
I want to solve two equattions which has five variable, so I want to provide ranges for three variables and get all the solutions.
3 variable with ranges are x4, x5 and z4, and I want to find corresponding solution for z5 and G. (Actually I have a formula which I nedd to equate with the real and imaginary part of a complex number)
I have tried this way-
x4=pi/36:pi/9:pi/2;
x5=pi/6:pi/9:pi/2;
z4=60:20:80;
for a=1:length(z4)
for b=1:length(x4)
for c=1:length(x5)
ZL=61.5-1i*47.4;
YL=1/ZL; % to be equated with its conjugate
GL=real(YL);
BL=imag(YL);
syms z5 real
syms z55 real
assume( z5 > 0)
syms G real
assume( G>0)
y4=1./z4;y5=1./z5;
ya(a,b)= -1i.*y4(a).*cot(x4(b)) % Formula -I
yb(c)=vpa((y5).*(G + 1i.*y5.*tan(x5(c)))./(y5+ 1i.*G.*tan(x5(c)))) %Formula-2
yeq(a,b,c)=ya(b)+yb(c) %sum
yeqR=real(yeq)
yeqI=imag(yeq)
eqn=[yeqR==GL, yeqI==-BL]
var=[G z5]
s=solve(eqn, var)
G1=s.G
z55=s.z5
end
end
end
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Hedayat
Hedayat 2018-11-13
Thanks KSSV,
below is the eqns, I have 5 variables and two eqns, so I have to assume 3 variables. (Later I will see if solutions are feasable or not)
ya= - i*y4*cot(x4)
yb= (y5 * (G+ i *y5* tan(x5))) / (y5+ i G* tan(x5) )
yeq=ya+yb
yL=1/(61.5-i*47.4)
Solve(yeq=yL*)
KSSV
KSSV 2018-11-13
What are the unknowns in the above? YOu can solve it with hand first..equate complex and real parts...and these two parts should be solved for unknowns.

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Hedayat
Hedayat 2018-11-13
Thank you again KSSV,
I need values for G and y5, and I want to sweep y4,x4 and x5, as I mentioned in main post. it wil not always yield a desired solutions. For example, I need a value of y5 in the range of 20-120 and G>0. Plus,based on these results, I have to add other complicated equations that too have some constraints , and this is why I am avoiding hand calculations.

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