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annotate four.m @ 1031:2ef20d00b386 feature/advectionRV

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For easier comparison, return both the first order and residual viscosity when evaluating the residual. Add the first order and residual viscosity to the state of the RungekuttaRV time steppers
author Vidar Stiernström <vidar.stiernstrom@it.uu.se>
date Thu, 17 Jan 2019 10:25:06 +0100
parents f6ada1719420
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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598
f6ada1719420 Add functions for calculating fourier transforms
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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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9
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10 u_hat = fftshift(u_hat);
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11
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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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15
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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