How can I find the index of a specific element in an array

I have a vector T of size 1 by 30. The values of its elements start from zero and go to a maximum value and then decay back to zero.

How can I find the index of the element that satisfies <= .05 * R only in the decaying region of T?

R = 5000;
T = [0	8	39.3	103	236.5	511.7	1026.1	1906.9	3148.7	 4293 	 4011.9	 2628.4  	 1037.4	 203.7	 28.6	 9.4	 4.2	 1.4	 1.3 	0.6	 0.1	0	0	0	0	0	0	0	0	0] 

Thanks

Answer 1

[Walter Roberson]

R = 5000;
T = [0	8	39.3	103	236.5	511.7	1026.1	1906.9	3148.7	 4293 	 4011.9	 2628.4  	 1037.4	 203.7	 28.6	 9.4	 4.2	 1.4	 1.3 	0.6	 0.1	0	0	0	0	0	0	0	0	0];
[~, maxidx] = max(T);
idx = find( (T <= 0.05 * R) & (maxidx <= 1:length(T)) )

idx = 1×17

14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

[Rayan Glus]

Thank you so much.

Answer 2

[KSSV]

R = 5000;

T = [0	8	39.3	103	236.5	511.7	1026.1	1906.9	3148.7	 4293 	 4011.9	 2628.4  	 1037.4	 203.7	 28.6	 9.4	 4.2	 1.4	 1.3 	0.6	 0.1	0	0	0	0	0	0	0	0	0] ;
x = 1:length(T);
%Get max value from T 
[val,id] = max(T) ; 
% Condition 
idx = find(T<=0.5*R) ;
% Pick only those greater then id 
idx(idx<id)=[];

plot(x,T)
hold on
plot(x(idx),T(idx),'*r')

[Rayan Glus]

Thank you for your answer. Idx starts from 13 though instead of 14.