Dear Conrad,
my email is [email protected] <mailto:[email protected]> Take care! Peter From: 'Conrad Schiff' via sympy <[email protected]> Sent: Wednesday, January 22, 2025 11:28 AM To: [email protected] Subject: Re: [sympy] trigsimp, assumptions, and vector magnitudes Thank you, Peter, for both your interest and for pointing me to another place to ask the question. I certainly would like to see what you are doing with the mechanics module so perhaps you can also point me to your work. Conrad _____ From: [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > on behalf of [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > Sent: Wednesday, January 22, 2025 2:22 AM To: [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > Subject: RE: [sympy] trigsimp, assumptions, and vector magnitudes Dear Conrad, I have never seen this range restriction – but then again I use mostly a sub library of sympy, called sympy.physics.mechanics (to set up symbolic equations of motion of multibody systems), so I am no sympy expert at all! Maybe you could ask your question here, too: https://github.com/sympy/sympy Peter From: 'Conrad Schiff' via sympy <[email protected] <mailto:[email protected]> > Sent: Wednesday, January 22, 2025 2:28 AM To: [email protected] <mailto:[email protected]> Subject: Re: [sympy] trigsimp, assumptions, and vector magnitudes Thank you, Peter but there is not quite what I was looking for. Technically your result simply proves that the square root of the square of a real number x is the absolute value of x (\sqrt{x^2} = |x| for x \in reals). Or in your terms: test = |sin(INC)|/\sqrt{sin(INC)^2} for INC real is always, identically, equal to 1. For my case, sin(INC)/|sin(INC)| is what I am looking at (i.e., the numerator has no absolute value), and it is equal to 1 for my assumptions but how can sympy know that without knowing that I've restricted INC to the range [0,\pi]? If, for example, INC were in the range [\pi,2\pi] then sin(INC)/|sin(INC)| = -1. If there is a way to say something like: INC = sm.symbols(‘INC’, real=True,range=[0,pi]) then I say that the result is proved. But I can't anything like this in the documentation (perhaps I simply don't know where to look). Conrad _____ From: [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > on behalf of [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > Sent: Tuesday, January 21, 2025 9:39 AM To: [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > Subject: RE: [sympy] trigsimp, assumptions, and vector magnitudes I guess sympy does not know that INC is real and sin(INC) > 0. I just tried: INC = sm.symbols(‘INC’, real=True) test = sympy.Abs(sympy.sin(INC)) / sympy.sqrt(sympy.sin**2(INC)) test = 1 was the result, as expected From: 'Conrad Schiff' via sympy <[email protected] <mailto:[email protected]> > Sent: Tuesday, January 21, 2025 2:57 PM To: [email protected] <mailto:[email protected]> Subject: [sympy] trigsimp, assumptions, and vector magnitudes I am writing a textbook on orbital mechanics and I would like to use sympy for certain calculations (e.g., deriving expressions for certain vectors in terms of Keplerian orbital elements) so that the readers realize the power of sympy. I have a specific problem I am hoping this group could help me with as I am also fairly new to sympy. Here is a minimum working example: ******************************** from sympy import * A, INC = symbols('A INC') zxh = Matrix([[-sin(A)*sin(INC)], [cos(A)*sin(INC)], [0]]) ******************************** At this point, I want to unitize 'zxh' so that the sin(INC) divides out. This is a legitimate step since the range of INC is restricted to 0 to \pi and the sin(INC) is always non-negative (I am ignoring the singularities on the boundaries of 0 and \pi). I tried the following but I get the errors below. Some help in coaxing sympy to do what I know can be done would be appreciated. ******************************** mag2_zxh = trigsimp(zxh.dot(zxh)) -> gives sin**2(INC) mag_zxh = sqrt(mag2_zxh) -> gives sqrt(sin(INC)**2) zxh/mag_zxh -> gives Matrix([[-sin(A)*sin(INC)/sqrt(sin(INC)**2)], [sin(INC)*cos(A)/sqrt(sin(INC)**2)], [0]]) ******************************** How can I coax sympy into recognizing that "sin(INC)/sqrt(sin(INC)**2) = 1"? Thanks for any help, Conrad Schiff, PhD Professor of Physics Capitol Technology University -- 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] <mailto:[email protected]> . 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