Problem 1954. Write a cubic formula function

Created by Tyler

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Create a function that will output the three roots of a cubic equation specified by the 4 coefficients listed as input. The output should be sorted using the "sort" function of matlab, to be consistent. Also, the output need only be accurate to the 4th decimal place, and the input "A" will always be non-zero and real.

Example:

A*x^3+B*x^2+C*x+D=0 --> [A,B,C,D]

x^3-6x^2+11x-6=0 --> [1,-6,11,-6]

cubicFormula([1,-6,11,-6]) --> [1,2,3]

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Last Solution submitted on Jan 12, 2024

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3 Comments

Alfonso Nieto-Castanon on 22 Oct 2013

the "sorted" requirement is problematic, I would suggest you drop this requirement and simply resort the output of cubicFormula after (not before) rounding to four digits (and apply the same logic to your testsuite)...

J.R.! Menzinger on 29 Oct 2013

is there maybe a several problem with the sorting method you describe/need?? :-/

Rafael S.T. Vieira on 5 Sep 2020

The problem requires abs as 'ComparisonMethod' for sorting and the non-conjugate transpose. That's a pain that I have just become aware: ' is the conjugate transpose, and .' is the non-conjugate transpose. The conjugate operator changes the signs of complex roots.

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Problem 1954. Write a cubic formula function

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Problem 1954. Write a cubic formula function

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