How to get interval of X for a certain value of Y in a plot or array.

I am interested in getting an interval of X values, for example, [Xmin , Xmax] after specifying a value of Y for example 0.3.

Answer 1

[Walter Roberson]

idx = find(y >= 0.3);
xmin = x(idx(1));
xmax = x(idx(end));