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- - **2 * 2 * 2 * 2 or pow(2, 4)?**
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2 * 2 * 2 * 2 or pow(2, 4)?Hi ,
I hope this isn't too trivial to ask, but I'm evaluating a polynomial that involve lots of terms like x^2y^2z^3, and although I can use the power function pow(a, b), I wonder if just writing x*x*y*y*z*z*z for example wouldn't be more efficient than pow(x, 2)*pow(y, 2)*pow(z,3). Or is it all the same? Thanks, - Olumide |

Re: 2 * 2 * 2 * 2 or pow(2, 4)?Olumide wrote:
> I hope this isn't too trivial to ask, but I'm evaluating a polynomial > that involve lots of terms like x^2y^2z^3, and although I can use the > power function pow(a, b), I wonder if just writing x*x*y*y*z*z*z for > example wouldn't be more efficient than pow(x, 2)*pow(y, 2)*pow(z,3). > Or is it all the same? There is no way to tell a priory. You have to measure. However, if your polynomial has "lots of terms" like those, you might want to try the Horner scheme of evaluating polynomials: a_5 x^5 + a_4 x^4 + a_3 x^3 + a_2 x^2 + a_1 x^1 + a_0 can be rewritten as ( ( ( ( a_5 * x + a_4 ) * x + a_3 ) * x + a_2 ) * x + a_1 ) * x + a_0 which uses only 5 multiplications and 5 additions. Best Kai-Uwe Bux |

Re: 2 * 2 * 2 * 2 or pow(2, 4)?Kai-Uwe Bux wrote:
> Olumide wrote: > >> I hope this isn't too trivial to ask, but I'm evaluating a polynomial >> that involve lots of terms like x^2y^2z^3, and although I can use the >> power function pow(a, b), I wonder if just writing x*x*y*y*z*z*z for >> example wouldn't be more efficient than pow(x, 2)*pow(y, 2)*pow(z,3). >> Or is it all the same? > > There is no way to tell a priory. You have to measure. > > However, if your polynomial has "lots of terms" like those, you might want > to try the Horner scheme of evaluating polynomials: > > a_5 x^5 + a_4 x^4 + a_3 x^3 + a_2 x^2 + a_1 x^1 + a_0 > > can be rewritten as > > ( ( ( ( a_5 * x + a_4 ) * x + a_3 ) * x + a_2 ) * x + a_1 ) * x + a_0 > > which uses only 5 multiplications and 5 additions. > > > Best > > Kai-Uwe Bux Which is also an easy way to convert a string representation of a number into the number itself :-) -- Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/> |

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