how to find elements in an array

Given this:

x = 1:100; 
y = 201:300; 
a = 250;

I know that

x(y==a)

will return 50, the value of x corresponding to the y index where y = a. Now if a has multiple elements, I'd like to find all the values of x corresponding to all the values of y where y equals any of the values in a. For example, if

a = [250; 215; 283];

I'd like to efficiently get the array [50; 15; 83]. How can I do this?

Answer 1

[Azzi Abdelmalek]

x = 1:100; 
y = 201:300; 
a = [250; 215; 283];
out=x(ismember(y,a))

[Chad Greene]

Brilliant, thank you!

Answer 2

[Thomas]

 x = 1:100;
 y = 201:300;
  a=[ 215 250 283];

c=ismember(y,a)
x(c)

should give you

 15 50 83

[Chad Greene]

thanks Thomas!