def add_variables(vars)
      # Store all the variables in the model
      GLPK.glp_add_cols(@ptr, vars.length)
      vars.each { |var| store_variable var }
    end
def add_variables(vars)
      # Store all the variables in the model
      GLPK.glp_add_cols(@ptr, vars.length)
      vars.each { |var| store_variable var }
    end
Add multiple variables to the model simultaneously