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annotate +time/+expint/Magnus_4.m @ 696:7c16b5af8d98 feature/quantumTriangles

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Add Jonatans symbolic lifehax
author Ylva Rydin <ylva.rydin@telia.com>
date Thu, 05 Oct 2017 18:04:23 +0200
parents bc39bb984d88
children
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1 % Takes one time step of size k using a fourth order magnus integrator
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2 % starting from v_0 and where the function F(v,t) gives the
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3 % time derivatives.
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4 function v = Magnus_4(v, D, t , k , matrixexp ,tol)
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8 if isa(D,'function_handle')
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9 c1 = 1/2 - sqrt(3)/6;
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10 c2 = 1/2 + sqrt(3)/6;
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12 A1 = D(t +c1*k);
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13 A2 = D(t + c2*k);
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14 Omega = 1/2*(A1 + A2) + sqrt(3)*k/12*(A1*A2-A2*A1);
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15 else
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16 Omega = D;
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17 end
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20 switch matrixexp
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21 case 'expm'
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22 v = expm(k*Omega)*v;
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23 case 'Arnoldi'
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24 v = time.expint.expm_Arnoldi(-Omega,v,k,tol,100);
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25 otherwise
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26 error('No such matrix exponential evaluation')
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28 end
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29 end