Explicit solution could not be found, using solve()

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);

Answer 1

[Walter Roberson]

This appears to be the same bug as https://www.mathworks.com/support/bugreports/677110 except no trig is involved.

Workaround:

Call the MuPAD symbolic engine directly. For example,

>> S = evalin(symengine,'solve([p1-y1,p2-y2,p3-sin(y3)],[y1,y2,y3])')

[Trevor Gates]

Thank-you, that solved the problem!