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| Interpolation http://forum.alglib.net/viewtopic.php?f=2&t=374 |
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| Author: | favour [ Thu Jun 02, 2011 4:55 pm ] |
| Post subject: | Interpolation |
Hi every one, I need to use Spline&& polynomial && regression interpolation in C#. how can i do that? is there any example to help me? Thankssss |
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| Author: | Sergey.Bochkanov [ Thu Jun 02, 2011 6:02 pm ] |
| Post subject: | Re: Interpolation |
You can find some information in the ALGLIB Reference Manual: http://www.alglib.net/translator/man/ma ... t_spline1d http://www.alglib.net/translator/man/ma ... nit_polint http://www.alglib.net/translator/man/ma ... unit_lsfit If you still have questions, feel free to ask them here. |
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| Author: | favour [ Fri Jun 03, 2011 2:58 am ] |
| Post subject: | Re: Interpolation |
Many thanks :) I actually impressed when i saw this powerful library. I have two question at the moment : 1- I entered this code : Code: alglib.spline1dinterpolant output; double[] x = new double[] { -2, -1, 0, 1, 2 }; double[] y = new double[] { 4, 1, 0, 1, 4 }; alglib.spline1dbuildakima(x, y, out output); The out put is {4,-4,1,0,1,-2,1,0,0,0,1,0,1,2,1,0}. it means that my equation curve is : f(x) = 4 - 4x + x^2 +x^4 - 2x^5 + x^9 + x^11 + 2x^12 + x^13 ??? 2- My second question is about my request: I have 2 arrays x and y which show the coordinate. the distance between them are not same. Which function is then best fit Spline Interpolation equation for me? Thanks Regards |
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| Author: | Sergey.Bochkanov [ Fri Jun 03, 2011 10:42 am ] |
| Post subject: | Re: Interpolation |
1. you should not work with contents of spline1dinterpolant structure directly - use ALGLIB functions to work with it. In particular, if you want to extract coefficients - use spline1dunpack - it provides convenient and 100% documented interface 2. you can use parabolically terminated cubic splines |
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| Author: | favour [ Sat Jun 04, 2011 4:52 am ] |
| Post subject: | Re: Interpolation |
Thanks for your help i have gotten one run-time error "Exception of type 'alglib+alglibexception' was thrown" i used Code: alglib.spline1dgriddiffcubic(mainPointX, mainPointY, out d1); the mainPointX and mainPointY have 31 double numbers.The numbers are : Code: double[] mainPointX = new double[] { 19, 20.5, 57, 144, 148, 154.5, 158.5, 178, 197.5, 269, 350, 379, 409, 473, 477.5, 485, 493, 497, 534.5, 572.5, 579, 584.5, 590, 605, 608, 609, 609, 609, 609, 609, 609 }; double[] mainPointY= new double[] { 99, 92.5, 91.5, 92.5, 92.5, 92.5, 92.5, 93.5, 93.5, 95.5, 96.5, 97.5, 97.5, 98.5, 98.5, 98.5, 98.5, 98.5, 99.5, 99.5, 99.5, 99.5, 99.5, 101.5, 103.5, 105.5, 107.5, 109.5, 111.5, 113.5, 115.5 }; what is wrong for me to get this error? Regards |
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| Author: | Sergey.Bochkanov [ Sat Jun 04, 2011 6:59 am ] |
| Post subject: | Re: Interpolation |
alglib.alglibexception class has msg field. If you read it, you will find description of situation which caused you program to abort. It tells that you have incorrect mainPointX - array size is correct, but data it holds are not. Several last elements are not distinct. |
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| Author: | favour [ Mon Jun 06, 2011 11:20 am ] |
| Post subject: | Re: Interpolation |
Yup your correct my numbers weren't distinct. Thanks Now i am looking for polynomial Regression, i used polynomialfit procedure to find equation line in n=4 for example. but i dont know how i can get equation line. the out parameter ( or 'p') is barycentric type. it has some parameters in the structure. which function can interpret this structure and the give me an equation line? another question is that, i want first deviation and second derivation values. In spline interpolation i used spline1dgriddiffcubic and spline1dgriddiff2cubic , which function here can easily give me these values? Thanks a lot Regards |
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| Author: | Sergey.Bochkanov [ Mon Jun 06, 2011 1:40 pm ] |
| Post subject: | Re: Interpolation |
barycentricbar2pow will convert your polynomial into power basis barycentricdiff can be used to calculate first derivative barycentricdiff2 can be used to calculate second derivative |
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