reconstruct a signal from modified approximation coefficients

Hi,

I have a problem when using the functions wrcoef and upcoef. Actually, I have a set of points that i call signal. I want to do a DWT of level 3 for this signal, I have thus a set of approximation coefficients (cA3) and a set of detail coeffiencient (cD3, cD2 and cD1). For the set of the approxiamtion coefficients (cA3), i need to modify it, so I have a new set cA3_new, and this set has a lenth greater than cA3 (the length of sA3 is 21 and cA3_new is 31). Now I want to reconstruct the approxiamtion part of the signal (which I call A). For the function wrecoef, I modified the 2 vectors (C and L), but A still takes the old ones, and thus for the reconstruction, A has the same length of the original signal, but normaly with the new coefficients (cA3_new), I should obtain A of length (31*2^3=31*8=248). And when using the function upcoef, with the 'db2' wavelet, the length of A become much larger than 248 and thus a border effects appear. Pls any help to solve my problem?