Optimization 如何在docplex（python）中启动区间变量边界？

我有以下OPL代码，需要在docplex（python）中实现它，我是该领域的新手

using CP;
dvar interval I1 in 0..20;
dvar interval I2 in 0..20;
dvar interval I3 in 0..20;

dvar int over1;
dvar int start1;
dvar int end1;

dvar interval artificialInterval;

maximize over1;

subject to
{

    over1==overlapLength(I1,I2);

    start1==maxl(startOf(I1),startOf(I2));

    end1==minl(endOf(I1),endOf(I2));

    startOf(artificialInterval)==start1;
    endOf(artificialInterval)==end1;

    over1==overlapLength(I3,artificialInterval);
} 

问题发生在行startOf（artificialInterval）=start1； 和endOf（artificialInterval）==end1

以下是我所做的：

mdl=CpoModel()

   I1=mdl.interval_var(define its parameters)
   I2=mdl.interval_var(define its parameters)
   I3=mdl.interval_var(define its parameters)

   over1=mdl.integer_var()
   start1=mdl.integer_var()
   end1=mdl.integer_var()

   artificialInterval=mdl.interval_var()

   over1=mdl.overlapLength(I1,I2)
   start1=mdl.max(mdl.start_of(I1),mdl.start_of(I2))
   end1=mdl.min(mdl.end_of(I1),mdl.end_of(I2))

   mdl.start_of(artificialInterval) =start1
   mdl.end_of(artificialInterval) =end1

   over1=mdl.overlapLength(I3,artificialInterval)

   obj = mdl.maximize(over1)
   mdl.solve()

这样我就有了语法错误“SyntaxError:cannotassigntofunctioncall” 所以我尝试使用set_start（start1），但我认为我也没有很好地使用它

如有任何提示，我们将不胜感激。 谢谢,

from docplex.cp.model import CpoModel 
mdl=CpoModel()

I1=mdl.interval_var(0,10)
I2=mdl.interval_var(0,10)
I3=mdl.interval_var(0,10)

over1=mdl.integer_var()
start1=mdl.integer_var()
end1=mdl.integer_var()

artificialInterval=mdl.interval_var()

mdl.add(over1==mdl.overlap_length(I1,I2))
start1=mdl.max(mdl.start_of(I1),mdl.start_of(I2))
end1=mdl.min(mdl.end_of(I1),mdl.end_of(I2))

mdl.add(mdl.start_of(artificialInterval) ==start1)
mdl.add(mdl.end_of(artificialInterval) ==end1)

mdl.add(over1==mdl.overlap_length(I3,artificialInterval))

obj = mdl.maximize(over1)
mdl.solve()

效果好多了