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9213 :: Solving cubic equations

• Levlan (orginal) [2022-06-06T22:51:32+02:00] view original

  how can I solve cubic equation in nim or by using a library from another language? looking for the most simple solution.

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• shirleyquirk (orginal) [2022-06-06T23:19:08+02:00] view original

  Sign up for an API account at Wolfram Alpha.

  roots(a*X**3+b*X**2+c*X+D)

  ...

  profit

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• Levlan (orginal) [2022-06-06T23:31:03+02:00] view original

  i hoped there is a library i can import and avoid writing the code by myself.

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• xigoi (orginal) [2022-06-07T01:04:52+02:00] view original

  It's a quite straightforward formula. Just writing it is much less effort than making a forum thread, waiting for responses, installing a library, reading its documentation and using it.

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• Clonk (orginal) [2022-06-07T10:47:10+02:00] view original

  Using Julia and Polynomials.jl (https://juliamath.github.io/Polynomials.jl/stable/) with Nimjl https://github.com/clonkk/nimjl) - I used this method in the past for Polynomial of any order

  import nimjl
  Julia.init(1):
    Pkg:
      add("Polynomials")
  
  jlUseModule("Polynomials")
  var p = Julia.Polynomial([1, 12, -4, 8])
  echo p
  #1 + 12*x - 4*x^2 + 8*x^3
  var s = Julia.roots(p)
  echo s
  # ComplexF64[-0.08080510243721191 + 0.0im, 0.29040255121860614 - 1.2093793342224015im, 0.29040255121860614 + 1.2093793342224015im]
  Run

  Using a raw Nim you probably want to start at : https://github.com/SciNim/polynumeric but it's more experimental.

  import polynumeric
  
  var p = Poly(cofs: @[8'f32, -4, 12, 1])
  var s = p.roots()
  echo s
  Run

  That said for finding read roots of a cubic polynomial it does the job. If you need more advanced functionality, feel free to open a PR. Like @xigoi said, the formulas aren't that complicated.

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• Levlan (orginal) [2022-06-07T16:43:02+02:00] view original

  Thank you :-)

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• elcritch (orginal) [2022-06-08T00:42:50+02:00] view original

  There also looks to be a wrapper for SymEngine derived from SymPy but in C++. Looks like it has a solve_poly as well as diff and a few others.

  https://github.com/SciNim/symengine.nim

  Example:

  let x = newSymbol("x") # symbol
  let y = newSymbol("y") # symbol
  let xPlusY = x + y # expression
  echo diff(x^2, x) # first derivative
  Run

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