Le forum de XCAS

Hi,

Is there an absolute irreducibility check in giac/XCas? In maple we have AIrreduc to check absolute irreducibility. For instance I can do: Jose

Is it possible to use residue ring arithmetic in giac, e.g. instead of Q[x0,x1,x2] I want to do arithmetic in Q[x0,x1,x2]/<f1,f2> for some polynomials f1, f2. I can always artificially induce this, but many things may break if this is not internally encoded (for instance matrix arithmetic with entri...

Thanks fréderic. Though it seems to be a lot of work just for a list of monomials. I guess I will use it if the number of such monomials are rather long otherwise it will not be too expensive to just use "part".

I know this is an old thread, but I want to point out on something in the last answer of frederic. The proposed method does not necessarily give me the correct list. Consider the following for instance from giacpy import giac x,y,z=giac('x,y,z') P=x**2 + x +y Q=(P.ratnormal()) # here sommet is * (nu...

What did you try exactly? If I run linsolve(gb[0:2],vars[0:2]), I get [-16*t**2+8,-16*t+16] gb is already the solution. I tried linsolve(ideal, giac("[b_0_8,b_0_9]") Technically the solution is already in ideal (so of course I could choose these from ideal), but I guess the extra equations in the b...

Hi, I have a system of equations which are clearly linear with respect to some of the variables (in my problem these are b_0_8 and b_0_9). So technically one should be able to get the solution using only linsolve for solving only these variables. In giac I am able to arrive to the solution using Gro...

I kind of resolved this by just asking the indets. So I went to each of the elements of the list, step 2 (since the second entry is the multiplicity), and ask if indets have length 0, if so I know they are constant.

Hi, I want to be able to get the polnyomial factors of a polynomial but I'm not sure what is the best way to do this in giac or giacpy. So for instance I have a polynomial say 2/3*(x+y*x+3) and I use the factors command I get [2,1,x*y+x+3,1,3,-1] In my actual codes this polynomials could be really l...

Hi Bernard, My unknowns are x,y,z and w. I think the solutions are parametrizable surfaces, so it can be parametrized by at least 2 parameters and not less. So we could assume the unknowns to be say z and w. But here, giac is struggling to find a solution (computation in my laptop does not end). Edi...

Dear Frederic,

Thank you for your hard and amazing work! I confirm that this works for me (including the nauty functionality). Wonderful!

Jose

Hi, I have a system of equations over Q(rootof(z^3-2)) that if I give in maple I get solutions with different branches and some of them are given as algebraic numbers. The code in maple looks like this: p1 := 2*RootOf(_Z^3-2)^2*z*x^2+8*RootOf(_Z^3-2)^2*z^2*x+2*x^3*RootOf(_Z^3-2)+8*x^2*RootOf(_Z^3-2)...

Hi Luka,

Wonderful, thanks a lot!

Apologies, I should have thought of that, I missed this command in the manual.

Jose

Hi, After some computations with algebraic numbers (as floats with high precision) I obtain a polynomial whose coefficients I know are integer but because the computations are done with floats, giac/xcas will show the coefficients with the decimals. I want to know what is the best way to convert thi...

I just want to congratulate lukamar for such hard work. This is amazing!! Has one the option to compile giac without Nauty or other graph theory libraries? I think having these options are really what makes giac stands out compared to other CAS. e.g. compiling with/without Pari, Cocoa etc. So one ca...

Hi, I am having a rather unusual output from linsolve when trying to solve a system of linear equation over algebraic numbers. The system that I have is defined by a matrix and I want to solve the kernel of this matrix. The matrix is rather long (so it is not a good idea to put it in this forum) but...