fmindnd problem doesnt run

I have this code in MATLAB, it doesnt run,what is the wrong?

g=9.81;zo=50;vo=15;m=50;c=13;
z=@(t) -(zo+m/c*(vo+m*g/c)*(1-exp(-c/m*t))-m*g/c*t);
[xmin fval]=fminbnd(z,0,8)

Answer 1

[Star Strider]

It runs here —

g=9.81;zo=50;vo=15;m=50;c=13;
z=@(t) -(zo+m/c*(vo+m*g/c)*(1-exp(-c/m*t))-m*g/c*t);
[xmin fval]=fminbnd(z,0,8)

xmin = 1.2874

fval = -59.1178

Does it throw any errors?

The fminbnd functon is part of core MATLAB and was introduced before R2006a, so you should have it.

.

Answer 2

[John D'Errico]

Never just say something does not run, and nothing more. Would you tell your doctor that something seems wrong, and hope they can diagnose your problem over the phone without saying anything more? Surely not.

If you got an error, then report the entire error, so EVERYTHING in red.

Does your code run? We can test it in Answers itself.

g=9.81;zo=50;vo=15;m=50;c=13;
z=@(t) -(zo+m/c*(vo+m*g/c)*(1-exp(-c/m*t))-m*g/c*t);
format long g
[xmin fval]=fminbnd(z,0,8)

xmin = 
          1.28739311227159

fval = 
         -59.1178285772914

I'll add a few more lines to see what it found.

fplot(z,[0,8],'b')
hold on
plot(xmin,fval,'ro')

So indeed, it does run, and appears to have found the minimum of that function. How well did it do?

syms T
Z = z(T)

Z = 

If it has a (local) minimum, then you can differentiate it, and solve for a solution.

tmin = solve(diff(Z,T,1) == 0,'returnconditions',true)

tmin = struct with fields:
             T: - (50*log(327/457))/13 + (pi*k*100i)/13
    parameters: k
    conditions: in(k, 'integer')

So there are infinitely many solutions, but all of them are complex, except for the one where k==0.

subs(tmin.T,'k',0)

ans = 

tmin = double(ans)

tmin = 
          1.28739699998827

To within the tolerances provided to fminbnd, AND the capabilities of floating point arithmetic in double precision, fminbnd found a reasonable solution.