smallest n such that vector(n) < a

hi,

 is there a efficient way that given a vector "vec" whose elements are monotonic increasing i can find the smallest index such that vec(n) < a. where "a" is some given value.

[Image Analyst]

The smallest/lowest/first index will be the first one (index = 1) like Azzi said. But that is a trivial case and I think you actually mean the highest index, and that is what Wayne gave you code for. Like m = [11 12 13 14 15] and the value = 13.1. The lowest index where m < 13.1 is 1 and the highest is 3. Please confirm/clarify.

Answer 1

[Wayne King]

 x = 1:100;
 a = 50;
 [val,idx] = find(x<a,1,'last');

idx is the index of vec() and val is the value

If the values in the vector are monotonically increasing as you describe, then the 'last' option gives you the last index. Did you really mean you want the "smallest"?

Answer 2

[Azzi Abdelmalek]

v=[10 12  4  5 9 20]
idx=find(v<5,1)

[Azzi Abdelmalek]

If v is increasing, the first index, if it exist, must be 1