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I'm working on an optimization problem in PuLP and I have to enforce a daily minimum of shifts and a daily maximum of assigned shifts. I have the following constraints to ensure each day has a minimum and maximum of employees assigned on day shifts and night shifts ($D_{i,j}$ and $N_{i,j}$).

for j in days:
    m += lpSum(D[(i, j)] for i in employees) >= b_d           
    m += lpSum(D[(i, j)] for i in employees) <= b_d_max       
    m += lpSum(N[(i, j)] for i in employees) >= b_n           
    m += lpSum(N[(i, j)] for i in employees) <= b_n_max

I tried to write both these constraints in a single line as follows:

for j in days:
    m += b_d <= lpSum(D[(i, j)] for i in employees) <= b_d_max  
    m += b_n <= lpSum(N[(i, j)] for i in employees) <= b_n_max

However, the lower limit is not enforced now. Am I doing something wrong or is it just not possible to write the constraints like this in a single line?

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    $\begingroup$ As far as I know its not possible, you need one line per symbol (<=,==,>=). $\endgroup$ – Kuifje May 6 '20 at 13:01

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