Changes a single coefficient in the problem. If the coefficient does not already exist, a new coefficient will be added to the problem. If many coefficients are being added to a row of the problem, it may be more efficient to delete the old row and add a new row.

In the following, the constraint is introduced in the problem and then its linear coefficient for x is changed to 3:

p = xpress.problem ()
x = xpress.var ()
c = x + x**2 <= 3
p.addVariable (x)
p.addConstraint (c)
p.chgcoef (c,x,3)

problem.chgmcoef is more efficient than multiple calls to chgcoef and should be used in its place in such circumstances.

problem.addcols, problem.addrows, problem.chgmcoef, problem.chgmqobj, problem.chgobj, problem.chgqobj, problem.chgrhs, problem.getcols, problem.getrows.