MATLAB: Finding a value of x for a given y

matlab function

lets say i have x=[10:10:100];

y=[23 45 60 82 111 140 167 198 200 220];

and i want to use linear interpolation to approximate the value of x when y=80

i can use interp1(x,y,80) to find the value of y when x=80

how can i get the opposite??

interp1(y,x,80)

Use the interp1 (link) function:

x=linspace(0, 100, 100);
y = x.^2+6;
xi = interp1(y, x, 37)
xi =
     5.5448

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