fminbnd doesn't give correction solution?

[paul6]

I am testing to solve an equation y = x.^3 - 2*x.^2 - 58 using different
functions, only "fzero" gives correct solution. The test code is as follows.
I'm using 4.2.1 version. Thanks for any help!function
test_eqn%[z1,fv1,info1,out1] = fminbnd(@f2,1.5,6)   %[z2,fv2,info2,out2] =
fminbnd(@f2,1.5,6) [z1,fv1] = fminbnd(@f2,1.5,6);[z1,fv1] =
fminbnd(@f2,1.5,6); [z2,fv2] = fminbnd(@f2, 1.5, 6);[z3,fv3] =
fzero(@f2,[1.5 6]);[z4,fv4] = fminsearch(@f2,2);[z5,fv5] =
fminunc(@f2,5);fprintf('z1=%f, fv1=%f\n',z1,fv1);fprintf('z2=%f,
fv2=%f\n',z2,fv2);fprintf('z3=%f, fv3=%f\n',z3,fv3);fprintf('z4=%f,
fv4=%f\n',z4,fv4);fprintf('z5=%f, fv5=%f\n',z5,fv5);%% output from the above
solutions in Octave 4.2.1.% Only "z3" obtained from "fzero" is right.%
z1=1.500000, fv1=-59.125000% z2=1.500000, fv2=-59.125000% z3=4.665079,
fv3=0.000000% z4=1.333374, fv4=-59.185185% z5=1.333342,
fv5=-59.185185%=========================function y = f2(x)y = x.^3 - 2*x.^2
- 58;



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