# Three-point approximation

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 April 29, 2020, 04:48 Three-point approximation #1 New Member   Art Mis Join Date: Apr 2020 Posts: 6 Rep Power: 6 Hi there, I would like to use a three point approximation as a boundary conditions, but having an unequal space grid, so far I only found information about the central differences while using those grids. The very known relation is: f'(x) = [ -3f(x) + 4f(x+h) -f(x+2h) ] / (2*h) But how does the relation change for an unequal space grid (instead of h, I have h1 and h2) ? Thank you very much !

 December 18, 2020, 21:28 3 point formula with enequal spacing #2 New Member   sam Join Date: Jan 2011 Posts: 20 Rep Power: 15 Hi Artmis, The solution is quite simple. Fit a parabola that interpolates f(x), f(x+h1) and f(x+h2) at x, x+h1, and x+h2. Call this interpolated parabola fp(x). Then, fp'(x) is the expression you are looking for. The procedure is the same for higher orders as well. Best, Sam hunt_mat likes this.

 Thread Tools Search this Thread Search this Thread: Advanced Search Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Jack001 ParaView 0 April 7, 2016 10:05 potofus EnSight 2 April 6, 2016 07:26 Robert@cfd ANSYS Meshing & Geometry 20 November 11, 2011 04:59 Wantami FLUENT 0 July 18, 2011 05:11 anfho OpenFOAM Programming & Development 0 May 6, 2011 15:28

All times are GMT -4. The time now is 16:58.

 Contact Us - CFD Online - Privacy Statement - Top