If statement with constraint

[gabarlacchi]

Hi,
I'have a problem with a particularly constraint on my CSP problem.
My decision variable is a matrix, and i apply some constraints. One of this is:
for e in range(exams):
for a in range(columns):
for y in range(exams):
if y != e:
if time_table[y,a] > time_table[e,a]: #time_table -> decision matrix
model += time_table[e,a] >= time_table[e,a] + exams_duration[e];
It doesn't work. I saw that the problem is within the IF statement. I would like to know what i'm doing wrong. My problem is "scheduling exams in a period with a number of rooms (moreover exams_duration, rooms_capacity and so on)". I have to force that an exams scheduled in a particularly time, start after the duration of the previous exams, if it exists.
thanks for the help,
Regards
Gabriele

[ehebrard]

Hi Gabriele, An 'if' statement in python requires a Boolean value. If x and y are variables, then 'x < y' is an expression (i.e., a variable true if and only the constraint x < y is satisfied). You can express an implication using the fact that variables with Boolean domains are treated as 0/1 so x <= z enforce z to be true if x is true, and does nothing otherwise, which I believe is what you mean to do: model += (time_table[y,a] > time_table[e,a]) <= (time_table[e,a] >= time_table[e,a] + exams_duration[e]) Cheers,

…

On Mon, Jan 30, 2017 at 10:02 AM, barloccia ***@***.***> wrote: Hi, I'have a problem with a particularly constraint on my CSP problem. My decision variable is a matrix, and i apply some constraints. One of this is: for e in range(exams): for a in range(columns): for y in range(exams): if y != e: if time_table[y,a] > time_table[e,a]: #time_table -> decision matrix model += time_table[e,a] >= time_table[e,a] + exams_duration[e]; It doesn't work. I saw that the problem is within the IF statement. I would like to know what i'm doing wrong. My problem is "scheduling exams in a period with a number of rooms (moreover exams_duration, rooms_capacity and so on)". I have to force that an exams scheduled in a particularly time, start after the duration of the previous exams, if it exists. thanks for the help, Regards Gabriele — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#49>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAVBC9qeIMa9vfCulXcr1TTc0mw3IuYiks5rXac8gaJpZM4LxKpm> .

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-Emmanuel

[gabarlacchi]

It works! thank you very much for the quick answer, very nice.
Cheers
Gabriele