"Merge" quarterly and daily data

dear All,

suppose I have two types of data:

 Date_mv    MV
01/2000     12
01/2000     11
01/2000     13
... one line for every day in the first quarter of 2000 that I have data. 
01/2000     15
02/2000     16
...one line for every day in the first second of 2000 that I have data. 
02/2000     13
...

and

 Date_lev    LEV
1/2000        5
2/2000        6
3/2000        4
4/2000        5
1/2001        6

I now want to "match" and do simple computations where I need the corresponding quarterly LEV value for each daily MV value.

Both date vectors are stored in struct. so are the MV and LEV values, for which I have N each (for N companies).

Say I want:

 X(t) = MV(t)*LEV(t)-LEV(t-1)*MV(t-1)

While I conceptually understand what I want, I am not sure how to approach this in matlab. Can anyone help?

Thanks in advance!