Mercurial > repos > public > sbplib
diff +time/+expint/Magnus_4.m @ 510:71908bbce2e1 feature/quantumTriangles
tried to add 4th order magnus integrator which does not work
| author | Ylva Rydin <ylva.rydin@telia.com> |
|---|---|
| date | Fri, 02 Jun 2017 17:46:01 +0200 |
| parents | |
| children | 4ef2d2a493f1 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/+time/+expint/Magnus_4.m Fri Jun 02 17:46:01 2017 +0200 @@ -0,0 +1,20 @@ +% Takes one time step of size k using a fourth order magnus integrator +% starting from v_0 and where the function F(v,t) gives the +% time derivatives. +function v = Magnus_4(v,D, t , k) + +if isa(D,'function_handle') + % v = krylov(k*D(t +k/2*t),v); + c1 = 1/2 - sqrt(3)/6; + c2 = 1/2 + sqrt(3)/6; + + A1 = D(t +c1*k); + A2 = D(t + c2*k); + Omega = k/2*(A1 + A2) + sqrt(3)*k^2/12*(A1*A2-A2*A1); + v = expm(Omega)*v; +else + %v = krylov(k*D,v); + v = expm(k*D)*v; +end + +end \ No newline at end of file