Finding a value on a plot using code?

So I am plotting 2 matrices on a graph and need to find the values of time when the vout is at 90% and 10%, as vout is 1v I need the values of time when vout = 0.9 and vout = 0.1 but my matrix does not have absolute values at these points. Is there anyway I can just use the curve of best fit's value in the code?

I.E

matrix 1 - Vout = 1, 0.95, 0.92, 0.89, 0.82       need time value at 0.9v 
matrix 2 - Time = 1, 2   , 3   , 4   , 5

Answer 1

[dpb]

Inverse interpolation...

>> Vout = [1, 0.95, 0.92, 0.89, 0.82];
>>   Time = 1:5;
>> T90=interp1(Vout,Time,0.90)
T90 =
  3.6667