Wow, thanks! DG
Pauli Virtanen wrote: > ke, 2006-11-08 kello 16:08 -0800, David L Goldsmith kirjoitti: > >> Hi! I tried to send this earlier: it made it into my sent mail folder, >> but does not appear to have made it to the list. >> >> I need to numerically solve: >> (1-t)x" + x' - x = f(t), x(0) = x0, x(1) = x1 >> I've been trying to use (because it's the approach I inherited) an >> elementary finite-difference discretization, but unit tests have shown >> that that approach isn't working. >> > [clip] > > You could try to use some of the pre-existing www.netlib.org codes for > solving BVPs. This only requires writing a wrapper. > > However, I have written a wrapper for the COLNEW code, which is a > finite-difference method written by Ascher & Bader in '87, having an > adaptive mesh selection. You can find it here: > > http://www.iki.fi/pav/bvp > > As I understand, COLNEW does not have any special handling for singular > coefficients, but nevertheless it seems to be able to solve your > problem. The code goes as follows: > > ---------------------------------------------------- > import scipy as N > import bvp > > u0 = 1 > u1 = 2 > > def f(t): > return N.sin(2*t) > > def fsub(t, z): > u, du = z > return N.array([(f(t) + u - du)/(1-t)]) > > def gsub(z): > u, du = z > return N.array([u[0] - u0, u[1] - u1]) > > tol = [1e-5, 1e-5] > boundary_points = [0, 1] > > solution = bvp.colnew.solve(boundary_points, [2], fsub, gsub, > is_linear=True, tolerances=tol, > vectorized=True, maximum_mesh_size=300) > > import pylab > > x = solution.mesh > pylab.plot(x, solution(x)[:,0]) > pylab.savefig('solution.png') > ---------------------------------------------------- > > BR, > > Pauli Virtanen > > > ------------------------------------------------------------------------ > > ------------------------------------------------------------------------- > Using Tomcat but need to do more? Need to support web services, security? > Get stuff done quickly with pre-integrated technology to make your job easier > Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo > http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 > ------------------------------------------------------------------------ > > _______________________________________________ > Numpy-discussion mailing list > Numpy-discussion@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/numpy-discussion > -- HMRD/ORR/NOS/NOAA <http://response.restoration.noaa.gov/emergencyresponse/> ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Numpy-discussion mailing list Numpy-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/numpy-discussion
