Solving an equation with more than one unknown in matlab

Question

mandy 2015-3-24

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https://ww2.mathworks.cn/matlabcentral/answers/184703-solving-an-equation-with-more-than-one-unknown-in-matlab

回答： Star Strider 2015-3-24

I am trying to find the solutions to the following two equations but since Matlab reads line to line I don't know how to enter these two equations so that it understands what I am trying to input. My code is

a=((-u/(10*j))+(s/(100*-j)))/((1/(j*100))-(1/10)-(1/10*j))
u=(((a/(10*j))-10)/(((1/100*j))+(1/10*j)))
s=25*exp(j*30*pi/180);

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Answer 1

Star Strider 2015-3-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/184703-solving-an-equation-with-more-than-one-unknown-in-matlab#answer_172474

在 MATLAB Online 中打开

If you have the Symbolic Math Toolbox:

syms a u s 
eqn1 = a==((-u/(10*j))+(s/(100*-j)))/((1/(j*100))-(1/10)-(1/10*j));
eqn2 = u==(((a/(10*j))-10)/(((1/100*j))+(1/10*j)));
eqn1 = subs(eqn1, {u}, {(((a/(10*j))-10)/(((1/100*j))+(1/10*j)))});
eqns = subs(eqn1, {s}, {25*exp(j*30*pi/180)});
a = vpasolve(eqns, a)
u = vpa(subs((((a/(10*j))-10)/(((1/100*j))+(1/10*j))),{a},{a}))

produces:

a =
88.519552132457129958929869921769 - 19.064250734748366881795919457402i
u =
- 80.472320120415572689936245383426 + 108.24022794068033352890538132491i

Could be more efficient, but this is the end of my day and I’m tired.