求助 方程关于变量不可导如何求根问题

求方程 I(x>=3)*5-5=0的根,其中I(t)=1,若t为真；I(t)=0,若t为假。
我的程序如下
function [tst0]=tst(t)
tst0=double(t>=3)*5-5;

命令：t=fsolve(@(t) tst(t),0,optimset('Display','iter'));

运行结果如下：
                                        Norm of      First-order   Trust-region
 Iteration  Func-count     f(x)          step         optimality    radius
     0          2              25                             0               1

No solution found.

fsolve stopped because the problem appears regular as measured by the gradient,
but the vector of function values is not near zero as measured by the
default value of the function tolerance.
请问这怎么回事捏？