matlab大神,我求解非线性规划出现了问题.怎么画出f函数呢

matlab大神,我求解非线性规划出现了问题.怎么画出f函数呢
function f = fun(x)
f = (tan(x(1) - atan(0.5)) - tan(x(1))) * x(2) * cos(x(3));
A = [1 0 0;
0 1 0;
0 0 1];
b = [pi/2; 3.9; pi];
Aeq = [];
beq = [];
vlb = [0; 0; 0];
vub = [];
[x,fval] = linprog('f',A,b,Aeq,beq,vlb,vub)
求f的最小值