Error returned with solve function

Hello!

I'm a bit puzzled when trying to solve a simple equation, taken as an example from the Matlab documentation:

syms a b c x
solve(a*x^2 + b*x + c == 0)

This returns:

??? Error using ==> char Conversion to char from logical is not possible.

Error in ==> solve>getEqns at 189 vc = char(v);

Error in ==> solve at 67 [eqns,vars] = getEqns(varargin{:});

Quite the opposite to what the example displays.

How can I solve this? Uku

Answer 1

[Walter Roberson]

You are using an older version of MATLAB that evaluates the truth of the comparison expression (creating a logical) before it calls solve()

Alternately, you might have assignments to a, b, c, and x before the solve() call, and if those assignments are all numeric values then the "symbolness" of the variables would be over-written, leaving a*x^2 + b*x + c as being a numeric variable, whose numeric value would be compared to 0 and that result passed to solve()