Hey,(adsbygoogle = window.adsbygoogle || []).push({});

So I am trying to do a tri-quadratic curve fit (linear regression) in excel. I have successfully completed a bi-quadratic, and it is of the form:

x+x^2+y+y^2+x*y+b (b is calculated by LINEST in excel)

My attempt at a tri-linear was:

x^2+x*y+x*z+y^2+y*z+z^2+b (b is calculated by LINEST in excel)

This equation was fairly accurate for my first few data points in the 4-curve family of curves I am attempting to curve fit, but after that the accuracy plummets.

I am assuming I am on the right track with this, as I attained some initial accuracy, but this equation isn't 100% because I can see it failing. Any/all help appreciated.

Note: I attempted to use the equation on http://www.rmi.ge/~kade/LecturesT.Ka...adraticLEC.pdf

but it gave an extremely erroneous solution.

**Physics Forums - The Fusion of Science and Community**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Tri-quadratic equation setup?

Loading...

Similar Threads - quadratic equation setup | Date |
---|---|

Discriminant of a quadratic equation in 2 variables | Nov 9, 2011 |

Solving a set of quadratic equations | Apr 12, 2011 |

System of 4 quadratic equations with 4 unknowns | Nov 16, 2010 |

Existance of solutions to set of quadratic equations | Nov 3, 2010 |

Putting an equation in quadratic form | Apr 28, 2010 |

**Physics Forums - The Fusion of Science and Community**