Why should this be so difficult?Talith wrote:The biggest problem with this method is probably in factoring the cubic, ie finding the b_i s.
uncivlengr wrote:edit: I tried that equation, gmalivuk, and it seems to be off by a constant - there's no a0 in the remaining quadratic, so I'm guessing the issue is somewhere there.
uncivlengr wrote:Right - the issue is probably an issue with excel rounding values, then... the constants coming out of the equation are pretty large, but the discrepancy between the true roots and the ones I'm getting are small enough.
uncivlengr wrote:edit: aaaand the contractor just called and decided to just get an extra crane for the operation instead of using the bracing system I was working on, so none of the work I spent my Sunday doing matters anyway!
http://en.wikipedia.org/wiki/Casus_irreducibilis wrote:In algebra, casus irreducibilis (Latin for "the irreducible case") is one of the cases that may arise in attempting to solve a cubic equation with integer coefficients with roots that are expressed with radicals. Specifically, if a cubic polynomial is irreducible over the rational numbers and has three real roots, then in order to express the roots with radicals, one must introduce complex-valued expressions, even though the resulting expressions are ultimately real-valued.
EDIT]Okay, a previous post included a link to a site using the Newton-Raphson method with Excel (I didn't see it before), but why do they need to make it so difficult. Sheesh.[/EDIT]
DougAJ4 wrote:ftww - the blog that PM2Ring linked to (and apparently I am not allowed to link to) contains a spreadsheet with a Cubic function using the same method as you posted (and also a CubicC function that will find complex roots).
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