Is it possible to modify in place a row/column?
No. OSI Does not allow such a thing. You can add and remove rows/columns to a problem, but once it’s done, it is impossible to modify them.
I can’t add colums/rows
Columns that you add must refer to existing rows (and vice-versa). That means you first have to add empty rows if you want to add your column. If you absolutely want to be able to add a column that refers to non existing rows, it should be fairly easy: write a function that counts the maximum row refered by the column you add, and add as many empty rows as needed in your problem. Same goes for the rows.
How efficiently does yaposib access to solvers memory?
yaposib’s design has been driven by memory access efficiency. It is built on the top of the C++ OsiSolverInterface class of COIN-OSI. You can thus manipulate and modify the rows/columns of the same problem as fast as you would be able to do it with OSI using the class OsiSolverInterface.