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annotate four.m @ 835:008496ca38f3 feature/burgers1d

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Compute the residual in between each runge-kutta stage. Note: It is not clear whether the correct residual is used when computing the stages. Must investigate further.
author Vidar Stiernström <vidar.stiernstrom@it.uu.se>
date Thu, 13 Sep 2018 18:14:54 +0200
parents f6ada1719420
children
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1 % four returns the fourier transform u_hat of the function u and the frequencies w
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2 function [w, u_hat] = four(x, u)
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3 u_hat = fft(u);
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4
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5 N = length(x);
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6 L = x(end) - x(1);
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7
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8 k = shift_k(0:N-1);
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10 u_hat = fftshift(u_hat);
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12 dw = 2*pi/L;
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13 w = dw*k;
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14 end
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16 function k_shifted = shift_k(k)
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17 N = length(k);
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18 k_shifted = [-floor(N/2):-1, 0, 1:ceil(N/2)-1];
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19 end