This is now Trac#23993 <https://trac.sagemath.org/ticket/23993#ticket>, but deserves further discussion. I'll post something on sage-devel after thinking it out.
HTH, -- Emmanuel Charpentier Le dimanche 8 octobre 2017 20:59:26 UTC+2, Emmanuel Charpentier a écrit : > > Yet another datapoint : our interface to mathematica *can* be used to get > a solution. The problem I got was that the result can't be translated back > to Sage : Mathematica express its results as "rules" (e.g "var -> > expression" means "expression is a solution for var"). Manually translating > these rules gives the Sage expression of the solutions. > > HTH, > > -- > Emmanuel Charpentier > > Le dimanche 8 octobre 2017 11:59:33 UTC+2, Emmanuel Charpentier a écrit : >> >> Another datapoint : Sympy seems to be able to (slowly) solve this system, >> via : >> >> from sympy.solvers import solve as ssolve >> ssol=ssolve([e.rhs()-e.lhs() for e in [eq1,eq2,eq3]],[x,y,z]) >> >> The output can be converted to Sage via: >> >> Ssol=map(lambda S:map(lambda v,s:v==SR(repr(s)).simplify_full(), [x,y,z], >> S), ssol) >> >> HTH, >> >> -- >> Emmanuel Charpentier >> >> Le samedi 7 octobre 2017 20:19:55 UTC+2, Emmanuel Charpentier a écrit : >>> >>> Inspired by an as.sagemath question >>> <https://ask.sagemath.org/question/39040/solving-a-system-of-equations-small-known-number-hinders-the-solution/>, >>> >>> I tried to solve a not-so-simple system, and found that Sagemath (8.1beta7) >>> is currently unable to solve it : >>> >>> sage: var("x,y,z,K") >>> (x, y, z, K) >>> sage: xi=3/4 >>> sage: yi=0 >>> sage: zi=0 >>> sage: eq1=K==y^2*z/x^2 >>> sage: eq2=xi+yi==x+y >>> sage: eq3=2*xi+yi+2*zi==2*x+y+2*z >>> sage: solve([eq1,eq2,eq3],[x,y,z]) >>> [] >>> >>> However, this system *is* solvable : one ca solve [eq2,eq3] for y and z, >>> substitute the (only) solution in eq1 and solve it for x, which turns out >>> to give three solutions (looking suspiciously close to the solution of a >>> cubic) ; substituting each of these solutions in the solutions for y and z >>> gives three (not-so-light) solutions for the system. >>> >>> Trying to solve it with maxima invoked from sage also fails : >>> >>> sage: %%maxima >>> ....: display2d:false; >>> ....: xi:3/4$ >>> ....: yi:0$ >>> ....: zi:0$ >>> ....: eq1:K=y^2*z/x^2$ >>> ....: eq2:xi+yi=x+y$ >>> ....: eq3:2*xi+y+2*zi=2*x+y+2*z$ >>> ....: sys:[eq1,eq2,eq3]; >>> ....: sol:solve(sys,[x,y,z])$ >>> ....: l:length(sol)$ >>> ....: l; >>> ....: >>> false >>> >>> >>> >>> >>> >>> >>> [K=(y^2*z)/x^2,3/4=y+x,y+3/2=2*z+y+2*x] >>> >>> >>> 0 >>> >>> Printing the value of sys shows that it is defined. Printing the length >>> of the solution that this solution is indeed has length 0 (no solution) and >>> that failing to print it is *not* an interprocess communication problem >>> caused by a "too long" result. >>> >>> However, when running the same Maxima program in the interpreter from >>> the command line does give a solution (much more massive, by the way, that >>> the one obtained manually). See enclosed source and output, obtained by : >>> >>> cat ttstSolve.mac | sage --maxima > ttstSolve.out >>> >>> Therefore, the problem seems to exist in Sage's interface to maxima, not >>> in Maxima itself. >>> >>> Perusing the list <https://trac.sagemath.org/wiki/symbolics> of >>> symbolics tickets didn't allow me to recognize this bug. A cursory >>> inspection of Maxima-related tickets gave no more results. >>> >>> Questions : >>> 1) Is this a new bug ? >>> 2) Does it deserve a ticket ? >>> >>> For what it's worth, Mathematica has no problem solving the system (in >>> its native interface) and gives relatively lightweight solutions ; I failed >>> to obtain solutions from fricas, giac and maple, as well as to get >>> Mathematica's answer through its Sage interface. >>> >>> HTH, >>> >>> -- >>> Emmanuel Charpentier >>> >>> >>> -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at https://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.
