# some problem about caculation of quadrature

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 March 8, 2006, 04:10 some problem about caculation of quadrature #1 ztdep Guest   Posts: n/a Hell0: ervery one ! i want to compute the integeral of some variable over whole domain, the intergral need a high resolution gauss quadrature method, but i only have the varible value on my two dimensional grid points, the gauss quadrature need the value at the gauss quadrature points, then how should i know it. it is a two diemsional rectangle domain. regards

 March 8, 2006, 11:04 Re: some problem about caculation of quadrature #2 al Guest   Posts: n/a maybe you should use a spectral method.

 March 8, 2006, 11:10 Re: some problem about caculation of quadrature #3 ztdep Guest   Posts: n/a can spectral method caculate the integral

 March 8, 2006, 15:25 Re: some problem about caculation of quadrature #4 al Guest   Posts: n/a you wrote: "..I want to compute the integeral of some variable over whole domain, the intergral need a high resolution gauss quadrature method, but i only have the varible value on my two dimensional grid points, the gauss quadrature need the value at the gauss quadrature points, then how should i know it. " I am assuming that your solution/ or your points are given in terms of a low order method, i.e. FDM or FVM. Your problem is that you want to use a high order quadrature for computing the integral (I dont know why). Of course, your quadrature point does not coincide with your FD/FV points. So, my suggestion was if you require high accuracy you should consider a high order method for example galerkin spectral method, or variations depending on your problem for computing your solution. So, by the way why you want to use a gauss quadrature ? if you have your points uniform distributed you can use a rectangular integration rule or equilavents.

 March 8, 2006, 18:58 Re: some problem about caculation of quadrature #5 ztdep Guest   Posts: n/a thank you very much! i am doing a Galerkin projection onto the POD eigenmode, the projection is a integral, and it is nesessary to evaluate it with a high resolution scheme! the pod eigenmode was obtained from the FVM solutions. regards

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