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annotate four.m @ 774:66eb4a2bbb72 feature/grids

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Remove default scaling of the system. The scaling doens't seem to help actual solutions. One example that fails in the flexural code. With large timesteps the solutions seems to blow up. One particular example is profilePresentation on the tdb_presentation_figures branch with k = 0.0005
author Jonatan Werpers <jonatan@werpers.com>
date Wed, 18 Jul 2018 15:42:52 -0700
parents f6ada1719420
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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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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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