How can I make the dimensions to agree

IR = find(abs(TTB1(:,1)-CR)<0.1, 1, 'first');%interpulated row -> (IR) for proof
IC = find(abs(TTB1(1,:)-TR)<0.1, 1, 'first')
dfdC = diff(TTB1(IR,:))
dfdT = diff(TTB1(:,IC));
f = intersect(dfdC,dfdT)
C3 = (f+((C2(i)-CR)*dfdC)+((tempexp-TR)*dfdT));

[Rik]

The two parts you are trying to add up are not the same size, which makes sense because they are derived from a column vector and a row vector. Without knowing what your goal is and plausible data to test your code there is little we can do for you.

Also f might not have the size you expect, should there be some implicit expansion to fix that?