Why does my code take forever to give a result?

Question

Enzo Berberi 2022-5-20

0
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回答： Abhiram V. P. Premakumar 2022-5-20

Hello,

I created this code in order to find the capacities of 10 capacitors for a given circuit. But when I run it, it takes a lot of time to run and after 30 minutes it gives back "Warning : Solutions might be lost." Does anybody know why is that?

%calculates capacitance in series
s = @(varargin) 1/sum(1./[varargin{:}]);
%calculates capacitance in parallell
p = @(varargin) sum([varargin{:}]);
%the system of 10 linear equations
syms c1 c2 c3 c4 c5 c6 c7 c8 c9 c10
eqn1 = p(c1,s(c5,c2),s(c8,c3),s(c9,c4)) == 0.3;
eqn2 = p(c2,s(c5,c1),s(c6,c3),s(c10,c4)) == 0.3;
eqn3 = p(c3,s(c8,c1),s(c6,c2),s(c7,c4)) == 0.3;
eqn4 = p(c4,s(c7,c3),s(c10,c2),s(c9,c1)) == 0.3;
eqn5 = p(c5,s(c1,c2),s(c9,c10),s(c8,c6)) == 0.25;
eqn6 = p(c8,s(c9,c7),s(c1,c3),s(c5,c6)) == 0.25;
eqn7 = p(c9,s(c1,c4),s(c8,c7),s(c5,c10)) == 0.25;
eqn8 = p(c6,s(c10,c7),s(c2,c3),s(c5,c8)) == 0.25;
eqn9 = p(c10,s(c6,c7),s(c5,c9),s(c2,c4)) == 0.25;
eqn10 = p(c7,s(c3,c4),s(c8,c9),s(c6,c10)) == 0.25;
%the values of the 10 capacitors
sol = solve([eqn1, eqn2, eqn3, eqn4, eqn5, eqn6, eqn7, eqn8, eqn9, eqn10],[c1, c2, c3, c4, c5, c6, c7, c8, c9, c10]);
c1Sol = sol.c1;
c2Sol = sol.c2;
c3Sol = sol.c3;
c4Sol = sol.c4;
c5Sol = sol.c5;
c6Sol = sol.c6;
c7Sol = sol.c7;
c8Sol = sol.c8;
c9Sol = sol.c9;
c10Sol=sol.c10;

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Enzo Berberi 2022-5-20

normally it's a 10x10

bransa 2022-5-20

you can use Run & Time function in the Editor (in the drop down of the Run button) or wrap sections of your code in tic...toc to check how long each step is taking.

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Answer 1

Abhiram V. P. Premakumar 2022-5-20

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1723735-why-does-my-code-take-forever-to-give-a-result#answer_968360

在 MATLAB Online 中打开

Does you equation have feasible solutions?

I checked with a simple feasible problem, and it did give the correct answer.

Please check that as a first step.

clc;clear all;
%calculates capacitance in series
s = @(varargin) 1/sum(1./[varargin{:}]);
%calculates capacitance in parallell
p = @(varargin) sum([varargin{:}]);
%the system of 2 linear equations
syms c1 c2 
eqn1 = p(c1,c2) == 2;
eqn2 = s(c1,c2) == 0.5;
sol = solve([eqn1, eqn2],[c1, c2]);
c1Sol = sol.c1
c1Sol = 1
c2Sol = sol.c2
c2Sol = 1