MATLAB: Need help looking for local minimum on a parabola

finding minimumfunctionmhomeworkif statement

I was wondering if anyone would be able to help me out with this.. I need to use a function M file to determine the local minimum of a parabola where the critical points can also qualify as a minimum. Here is my code. Currently it is returning values without error but the values don't match any of my test data given by my instructor.
if true
  function c = myminimum(f, a, b)
syms x v w;
w=solve(diff(f(x)));
v=subs(f(x), w);
if (a<v && a<b);
  c=a;
elseif (b<v && b<a);
  c=b;  
else c=v;   
end
end
Here is the test data if that helps:
if truea = myminimum(@(x) x^2+1,-3,2)
a = 1
a = myminimum(@(x) x^2+6*x-3,-2,0)
a = -11
a = myminimum(@(x) -2*x^2+10*x,3,8)
a = -48
a = myminimum(@(x) -x^2+2*x+1,5,6)
a = -23

Best Answer

Do you have to use the if block?
The easy way is to use the min function:
syms x v w;
w=solve(diff(f(x)));
z = [w a b];
v=subs(f(x), z);
[q,k] = min(v);
c = v(k);
If you must use the if loop:
syms x v w;
w=solve(diff(f(x)));
z = [w a b];
v=subs(f(x), z);
if (v(1)<v(2) && v(1)<v(3));
  c=v(1);
elseif (v(2)<v(3));
  c=v(2);  
else
    c=v(3);
end
If it makes you feel any better, the ‘correct’ answer to this set:
a = myminimum(@(x) x^2+6*x-3,-2,0)
a = -11
is in error. The correct answer is -12, corresponding to the minimum of the parabola.
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