How can i interpolate 1-D data, whit y especified values?

Dear community

I want my interpolation to contain some specified values:

x = [1 2 3 4 6];
y = x^2;
xx = linspace(x(1),x(end),80)
vq = interp1(x,y,xx,'spline')

Let say that I want that vq contains y = 4.5 (or a set of values), and i have the x* value(s) that do y(x*) = 4.5 ( I alredy know that in this example y = 3.5 is a little off)

Thanks in advance.

Answer 1

[the cyclist]

Unless I'm missing something, it sounds like you just want to interpolate x from y, instead of y from x:

x = [1 2 3];
y = [1 4 9];

yq = y(1) : 0.5 : y(end);
xq = interp1(y,x,yq,'spline');
[xq' yq']

ans = 17×2

1.0000 1.0000 1.1875 1.5000 1.3667 2.0000 1.5375 2.5000 1.7000 3.0000 1.8542 3.5000 2.0000 4.0000 2.1375 4.5000 2.2667 5.0000 2.3875 5.5000

[camilo utrera]

Thanks you very much, I think I was a little cofused in how the problem was written.