how can i get value of 'a' at b=0.

   clc;
   close all;
   clear all;
   a=[5,11,15,18,22,30];
   b=[2,3,4,5,6,7];
   plot(b,a);

if i want value of 'a' at b=5.5 then i use 'interp1' function and i got correct value of 'a',

but how can i get value of 'a' at b=0.

[Jan]

The half of your code consists of unmotivated brute clearing. I recommend to avoid this in your real programs, at least the useless "clear all" when actually a "clear variables" is meant. But for posting in the forum, such general purpose overhead code is noise only.