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Ecco, a me che sono andato all’estero sta cosa dell”assegno di ricerca” continua a rovinarmi. Ho finalmente passato un concorso per la famigerata “entrata in ruolo” in Francia e per decidere lo scalino iniziale mi chiedono i contratti pregressi. Ecco che in Italia siamo ben attenti a chiamarlo “assegno di ricerca” (e non contratto di lavoro), a specificare che si tratta di un rapporto “non subordinato, senza vincoli di orario”, che, non sia mai, è “di diritto privato”…
Ecco che in Francia quello che in Italia è considerata la forma ufficiale di post-doc non mi vale piu un c–…. posso dirlo..? si lo dico, un cazzo, ed ora devo ripartire da zero.. tutto per l’ipocrisia italiana. .ma perché deve essere “di diritto privato” (ho lavorato per un’università pubblica!), “non subordinato” (ma va là!!), senza vincoli di orario (quanti week end e serate passate ad elaborare dati!).
Dibattito sullo spot della Chicco che “ironicamente”, invita a fare figli: https://www.youtube.com/watch?v=upxsL__Wm_U
Mentre è chiaro che l'obiettivo dell'azienda Chicco è di pubblicizzarsi e vendere pannolini & co, il tema rimane di forte attualità.. Ma che barba sta roba che per fare i figli ci devi avere casa, contratto a tempo indeterminato, macchina 7 posti, matrimonio da 30k € sulle spalle…
Al nostro secondo figlio già parenti e amici hanno lanciato qualche mugugno, al terzo sono arrivati a proporre l'aborto.
Perché li abbiamo fatti? Perché intorno a noi vediamo che gli altri li fanno, e senza alcun problema.
E no, non viviamo più in Italia.
JuMP (Julia for Mathematical Optimization) is an Algebraic Modelling Language (AML) that allows to write optimisation problems using a concise mathematical formulation, acting as interface to the specific solver engine API. For non-linear optimisation problems it allows to keep a high-level approach that doesn't require the modeller to compute the Jacobian or the Hessian.
It is developed by the MIT Operations Research Center and appeared in 2013 as an open source package of the relatively new Julia programming language.
GAMS (The General Algebraic Modeling System) does more or less the same things and appeared in the '70s as a project of the World Bank. GAMS is hence a very mature project (maybe too mature) with a lot of followers in the economic domain, where it is used mainly to solve equilibria problems.
This mini-tutorial is intended for gams users that want to try JuMP. There may be two reasons for someone to with to use JuMP instead of GAMS.
The most obvious one, even if often it isn't the key driver, is that GAMS is a commercial software while JuMP being open-source is free both as freedom and as a free beer.
While for GAMS a licence for the underlying solver engine is often included with a particular version of GAMS, JuMP would still require the user to buy a licence to use a specific commercial solvers. However JuMP interfaces with both GLPK (for linear and mixed-integer programming) and IPOPT (for non-linear optimisation) open-source solvers, both of which are top on their classes, leaving the necessity to acquire a licence for a commercial solver to niche cases.
The second reason (and, to me, the most important one) resides in the language features and in the availability of development environments. GAMS uses a VERY ODD syntax, somehow derived from the Cobol language, that is very distant from any programming language in use nowadays. For example a macro mechanism to provide an elementary way to structure the code in reusable components has been introduced only in GAMS 22.9. Its own editor is also very terrible, but as most text editors do not provide a GAMS syntax highlighting, it's still the most common way to code in GAMS.
JuMP, at the opposite, is both open source and it allow to write the model in a powerful general-purpose language like Julia
You have plenty of development environment to choose from (e.g. Jupiter, Juno), a clear modern language, the possibility to interface your model with third party libraries.. all of this basically for free.
It is also, at least for my user case, much faster than GAMS. Aside the preparation of the model to pass to the solver, where it is roughly equivalent, in the solver execution I can benefit of having on my system a version of IPOPT compiled with the much more performing ma27 linear solver, while for GAMS I would have to rely on the embedded version that is compiled with the MUMPS linear solver. That's part of the flexibility you gain in using JuMP in place of GAMS. That's said, for people that don't need such flexibility, the package automatically install a local pre-compiled version of the solver, so just adding the package relative to the solver is enough to start writing the model. Even more, for people that doesn't care too much about performances, there is a service on JuliaBox.com that allows to run Julia/JuMP scripts for free in the browser, without anything to install on the local computer.
So let's start. We will see how to code the trasnport.gms problem, the one that ship as default example in GAMS1), using JuMP. For a fictions product, there are three canning plants and three markets and the objective of the model is to find the optimal allocation of products between plants and markets that minimises the (transport) costs.
GAMS equivalent code is inserted as single-dash comments. The original GAMS code needs slightly different ordering of the commands and it's available at http://www.gams.com/mccarl/trnsport.gms
ok, I am an etranger, so no way I can run for the French Presidencial elections Still, I think I lived long enough in this country to have my own opinion on what could be done to improve the welfare of its citizens, in a gagnè-gagnè way that increases efficiency and make everyone better off.
So, these are my points.. I'll be very quick - time is a scarce resource - but if I'll have more time I'll expand it: