Thanks Leonid for this quick and helpful answer! I just have a few follow-up questions:

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On Thu, Feb 22, 2018 at 11:38 PM, Leonid Kovalev wrote: > In SymPy, polynomials have extra structure that distinguishes them from > generic expressions. a3 * t**3 + a2 * t**2 + a1 * t + a0 is an expression. > If you create a polynomial in t, it will print with the order of terms being > from highest to lowest. > > >>> p = sp.Poly([a3, a2, a1, a0], t) > >>> print(p) > Poly(a3*t**3 + a2*t**2 + a1*t + a0, t, domain='ZZ[a0,a1,a2,a3]') Ah, that's interesting! I was actually using a Jupyter notebook with MathJax output most of the time, and there this is not true! Same for the raw LaTeX output: >>> sp.latex(p) '\\operatorname{Poly}{\\left( a_{0} + a_{1} t + a_{2} t^{2} + a_{3} t^{3}, t, domain=\\mathbb{Z}\\left[a_{0}, a_{1}, a_{2}, a_{3}\\right] \\right)}' Is this a bug? > Also, the order can be specified in the print command > > >>> pprint(a3 * t**3 + a2 * t**2 + a1 * t + a0, order='grevlex') > 3 2 > a₃⋅t + a₂⋅t + a₁⋅t + a₀ > > > or, staying with str format, > > > >>> sstrrepr(a3 * t**3 + a2 * t**2 + a1 * t + a0, order='grevlex') > 'a3*t**3 + a2*t**2 + a1*t + a0' That's great, I think 'grevlex' is what I want! I was actually already playing around with 'lex', 'revlex' and 'grevlex', but I got confused at some point. It looks like this doesn't work if the highest power doesn't have a symbolic coefficient, e.g.: >>> sp.sstrrepr(t**2 + a1 * t, order='grevlex') 'a1*t + t**2' I assume there is a perfectly reasonable explanation for that, and in my case such expressions didn't actually appear yet, so that's fine for me. I think I will mainly use 'grevlex' with: sp.init_printing(order='grevlex') But when I'm dealing with expressions that have only the coefficients and no powers of t in them, e.g.: 3*a3 + 2*a2 + a1 ... then I'll temporarily switch: sp.init_printing(order='rev-lex') Or is this a bad idea? Or is there a better way to temporarily change the order? Is there a way to specify the order for a single Jupyter output cell? > The printing module has a number of printers which support a number of > settings. Thanks for the reference to http://docs.sympy.org/latest/modules/printing.html, that's a very helpful page. cheers, Matthias > On Thursday, February 22, 2018 at 2:02:20 PM UTC-5, Matthias Geier wrote: >> >> Dear SymPy list. >> >> I'm playing around with polynomials in the context of spline curves. >> >> I want to use a cubic polynomial with yet unknown coefficients like this: >> >> >>> import sympy as sp >> >>> t, a0, a1, a2, a3 = sp.symbols('t, a:4', real=True) >> >>> a3 * t**3 + a2 * t**2 + a1 * t + a0 >> a0 + a1*t + a2*t**2 + a3*t**3 >> >> The problem here is that the displayed order of terms is reversed, >> normally the highest power of t should come first. >> I guess this is because SymPy doesn't know that the coefficients a0 >> etc. are constants and shouldn't be treated like variables. >> So in fact this polynomial isn't sorted by powers of t but instead by >> the coefficients. >> >> Is there a way to get around this? >> >> At some later point, I have expressions like this (without t): >> >> a1 + 2*a2 + 3*a3 >> >> It would make sense in my case to also display them reversed like this: >> >> 3*a3 + 2*a2 + a1 >> >> Is it possible to create a new type of symbol with non-default ordering? >> Is it possible to define that this order is "ascending": a3, a2, a1, a0? >> It doesn't have to be a generic solution, I'm OK with having those 4 >> special symbols. >> >> Or is there an entirely different and much better way to do this? >> >> I know that I could just use a, b, c, d instead of a3, a2, a1, a0 and >> it would work, but I would really like to see the connection between a >> coefficient and its power of t. >> >> For the record, I also quickly tried to use IndexedBase to get a3, a2, >> a1 and a0, and it turns out that although the LaTeX display of the >> symbols looks the same (in text mode it's different), they are sorted >> differently. >> >> >>> b = sp.IndexedBase('b') >> >>> b[3] * t**3 + b[2] * t**2 + b[1] * t + b[0] >> t**3*b[3] + t**2*b[2] + t*b[1] + b[0] >> >> They are sorted after the powers of t, which isn't what I want, either. >> >> cheers, >> Matthias -- 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 sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAFesC-cN3_h-dVm854PeU%3Dkr3J%2Bhywyvkk0JBMbDrqQiRcbinA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.