Finding/ returning intermediate value in vector

Hi

Say I have a vector:

    x = [5 20 15 17]

Is there any way to access values with any intermediate index? For example x(2.5)=17.5 or x(1.37)=10.55? I realise I could interpolate or calculate it by ratios. I'm looking for the easiest way to do this.

I'm also looking for the other way around. Say I have a strictly increasing vector, is there any way to find position of a value? For example

    y = [1 5 7 14]

Is there a function such that: function(y, 3) = 1.5. (Is there any way to do this if it isn't strictly increasing/decreasing?)

Regards

Answer 1

[KSSV]

USe interp1. Read about it.

% Question 1
x = [5 20 15 17] ;
idx = 1:length(x) ;

interp1(idx,x,2.5)
interp1(idx,x,1.37)
% Question 2
y = [1 5 7 14] ;
x = 1:length(y) ;
interp1(y,x,3)