Yes, for now, Mul automatically distributes constants, so you have to use evaluate=False to factor out something like -1.
Aaron Meurer On Wed, Nov 4, 2015 at 5:13 AM, Hugh <[email protected]> wrote: > Thanks Aaron for pointing out the simplification section of the tutorial. > > Actually, collect(expr1, [x11, x12, x13]) does almost what I wanted. I > still need to factor a -1 from x12( -x21x33 + x23x31). How would you do it > using replace() like what I did? I also tried putting (x12*a).factor() as > the value for replace but that didn't work. I had to use Mul() with evaluate > = False to get it to do what I wanted. > > On Wednesday, 4 November 2015 06:19:34 UTC+8, Aaron Meurer wrote: >> >> A good start would be the simplification section of the tutorial >> http://docs.sympy.org/latest/tutorial/index.html. >> >> In this case, collect(expr1, [x11, x12, x13]) does what you want. >> factor() only does complete factorizations (into products of terms). >> This is explained in more depth in the tutorial. >> >> Aaron Meurer >> >> On Tue, Nov 3, 2015 at 2:47 PM, Hugh <[email protected]> wrote: >> > import sympy >> > sympy.init_session() >> > >> > >> > x11, x12, x13, x21, x22, x23, x31, x32, x33 = symbols('x_1:4(1:4)') >> > >> > A = Matrix(3,3,symbols('x_1:4(1:4)')) >> > expr1 = A.det() >> > >> > expr2 = x11*(x22*x33 - x23*x32) - x12*(x21*x33 -x23*x31) + x13*(x21*x32 >> > - >> > x22*x31) >> > >> > # How to get expr2 from expr1? >> > >> > I would like to use sympy to rewrite expressions just like how people >> > would >> > commonly do when writing proofs or doing homework. What are the >> > documentation that I must read so that I can be proficient at this? >> > >> > I've read the tutorial and some of the modules in the module reference >> > but >> > feel that I have just barely touched the surface of sympy's >> > capabilities. >> > For example, in the above code snippet, I don't know how to manipulate >> > expr1 >> > to get expr2. I thought expr1.factor() would work but it didn't. >> > >> > Please advise. >> > >> > -- >> > You received this message because you are subscribed to the Google >> > Groups >> > "sympy" group. >> > To unsubscribe from this group and stop receiving emails from it, send >> > an >> > email to [email protected]. >> > To post to this group, send email to [email protected]. >> > Visit this group at http://groups.google.com/group/sympy. >> > To view this discussion on the web visit >> > >> > https://groups.google.com/d/msgid/sympy/9cbb1995-3987-44f1-8c72-6de11e6a4013%40googlegroups.com. >> > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sympy. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/438ac161-214e-497d-964c-87900be74dcb%40googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAKgW%3D6LDOAcB81ON9m2a4T%3DKMOA2R64PNwqrmcGRrcN93WvFoA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
