Is it possible that no one knows the solution to my problem?

Let me simplify it:

time = [ 1.1 1.2 1.3 1.4 1.5]

voltage = [2 4 5 6 7]

if I type:

index = (time=1.1)

which should return 1

it return me:

Empty matrix 1 by 0

what could be the problem? for some numbers it works but for some it does not! is there any other way to fetch the index of some value in a matrix besides the "find" method.

please help and that u in advance