Expand one vector based on another

It was really difficult to come up with a proper title for this question and hence, difficult to google as well. Anyways, my problem is like this:

1. I have two vectors x and y
2. x(1), x(end), y(1) and y(end) never change
3. If I add one or more element, a = [x(1), x(end)] to x: how do I expand y accordingly? Is there a built-in function for this?

Some code to illustrate:

y = [1 2];
y = someFunc([1 2 3], y)

    y = [1 1.5 2]
y = [1 2];
y = someFunc([1 2.5 3], y)

    y = [1 1.75 2]

[Martin Rindarøy]

It seems like interp1 actually does exactly what I want. Silly me :)

Answer 1

[Ameer Hamza]

The following function will work for you

function z = someFun(y, y0)
  z = y0(1) + (y-min(y))./(max(y)-min(y))*(y0(2)-y0(1));
end

save it in your MATLAB path and call it as follow

y = [1 2];
y = someFun([1 2.5 3], y)