If you want to update certain OD pairs in the demand matrix, create a filter matrix with the same dimensions as the demand matrix and with the value 0 for all OD pairs that are to be saved unchanged to the results matrix.
1. Open the demand matrix you want to update ( Opening a Visum matrix).
2. Overwrite the value of all OD pairs which should remain unchanged with 0.
3. Save the filter matrix in $V or $O format (Saving matrices).
