Explicit solution could not be found, using solve()

Question

Trevor Gates 2017-7-9

0
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https://ww2.mathworks.cn/matlabcentral/answers/347911-explicit-solution-could-not-be-found-using-solve

编辑： Walter Roberson 2017-7-9

Hello,

I have a relatively simple problem that I am able to solve by hand (i.e. solution should be a_sol = s/2). However, when I try to solve it using the solve() function, I get the warning that an explicit solution could not be found. Below is the source code. Any advice would be greatly appreciated.

syms a s lambda1 lambda2;
obj = log(a);
cons1 = a;
cons2 = s/2 - a;
Lagrange = obj + lambda1*cons1 + lambda2*cons2;
eq1 = [char(diff(Lagrange, a)), '=0'];
eq3 = [char(diff(Lagrange, lambda1)), '>=0'];
eq4 = [char(diff(Lagrange, lambda2)), '>=0'];
eq3a = [char(diff(Lagrange, lambda1)*lambda1), '=0'];
eq4a = [char(diff(Lagrange, lambda2)*lambda2), '=0'];
eq6a = 'lambda1>=0';
eq6b = 'lambda2>=0';
[a_sol] = solve(eq1, eq3, eq4, eq3a, eq4a, eq6a, eq6b, a);