How to fix the error :Index exceeds matrix dimensions
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clear all; clc; close all
rho_sea=1027;
rho_air=1225;
g=9.8;
k=0.4;
alpha=0.008;
gamma=3.3;
delta_1=0.07;
delta_2=0.09;
Tp=[2 10 16];
fp=1./Tp;
T=2:1:70;
f_T=1./T;
u= [1.192 1.194 1.120];
z=[0.0021 0.0029 0.0033];
sigma= 2*pi*f_T;
k_nw=sigma.^2./g;
i_freq=1:69;
f1=0.03093;
c=1.1;
for i = 1:length(i_freq)
fi=f1.*c.^(i_freq-1);
end
%%% Dir(teta)
i_teta=1:36;
teta_i=10.*i_teta;
teta_i_cos=cos(2*teta_i);
for i = 1:length(teta_i_cos)
if teta_i_cos>0
dir_teta=0;
else
dir_teta= (2/pi())*(1/2)*(1+teta_i_cos);%cos^2(x) = (1+cos2x)/2
end
end
dir_teta;
%% T=2s
%mi
mi_2 = zeros(numel(teta_i),numel(sigma));
for i=1:length(sigma)
for j=1:length(teta_i)
mi_2(i,j)=(((g*z(1,1).*(k_nw(i).^2))./sigma(i).^2).*exp((k*sigma(i))./(k_nw(i).*u(1,1)).*cos(teta_i(j))));
end
end
mi_2;
mi_2(:,[37:69])=[];
% mp
mp_2=(1.2./k).*mi_2.*log(mi_2).*log(mi_2).*log(mi_2).*log(mi_2);
%%%%%%%%%%%%%%%%%%%%%%%%%%%% My problem below %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%beta
beta_2= zeros(numel(sigma),numel(teta_i));
Cf=(g.*T)./(2.*pi);
for i=1:length(sigma)
for j=1:length(teta_i)
beta_2(i,j)=(rho_air./rho_sea).*mp_2(i,j).*((u(1,1))./(Cf(i))).^2.*(1+cos(teta_i(i).*2)./2);
end
end
My mistake is on this line (third line from the bottom of the code):
beta_2(i,j)=(rho_air./rho_sea).*mp_2(i,j).*((u(1,1))./(Cf(i))).^2.*(1+cos(teta_i(i).*2)./2);
Thank you for your help
4 Commenti
Walter Roberson
il 12 Nov 2020
i_teta=1:36;
teta_i=10.*i_teta;
so teta_i is length 36.
T=2:1:70;
That is length 69
f_T=1./T;
so that is length 69
sigma= 2*pi*f_T;
and so is sigma.
for i=1:length(sigma)
for j=1:length(teta_i)
so i ranges from 1 to 69 and j ranges from 1 to 36
beta_2(i,j)=(rho_air./rho_sea).*mp_2(i,j).*((u(1,1))./(Cf(i))).^2.*(1+cos(teta_i(i).*2)./2);
^^^^^^^^^
i is at most 69. Consider in particular when i becomes 37. teta_i(i) would be teta_i(37) . But teta_i only has 36 elements.
Cf=(g.*T)./(2.*pi);
with T being length 69, Cf has 69 elements, so indexing Cf(i) with i to 69 is correct.
mi_2 = zeros(numel(teta_i),numel(sigma));
mi_2 is going to be initialized as 36 by 69.
for i=1:length(sigma)
i is going to be 1 to 69
for j=1:length(teta_i)
j is going to be 1 to 36
mi_2(i,j)=(((g*z(1,1).*(k_nw(i).^2))./sigma(i).^2).*exp((k*sigma(i))./(k_nw(i).*u(1,1)).*cos(teta_i(j))));
so you are going to assign up to mi_2(69, 36) when m_2 was initialized to 36 by 69. When you assign explicitly to a row or column that is larger than the existing size of the matrix, then the matrix is automatically expanded, so with the row index being up to 69, m_2 is going to expand up to 69 rows, giving you an m_2 that is 69 by 69 with the columns 37 and beyond left at their initial values of 0.
for i=1:length(sigma)
for j=1:length(teta_i)
so i ranges from 1 to 69 and j ranges from 1 to 36
beta_2(i,j)=(rho_air./rho_sea).*mp_2(i,j).*((u(1,1))./(Cf(i))).^2.*(1+cos(teta_i(i).*2)./2);
^^^^^^^^^
so you are going to access up to mp_2(69, 36) which is the part of mp_2 that had data written into it. That will be okay, but it does lead to the question of why you set up mp_2 to be 69 x 69 when you never use columns 37 to 69 from it.
=====
My recommendation would be that you rewrite your code to not use the variable names i or j as you are obviously losing track of what they mean. I suggest that you consider using names such as sigmaidx and thetaidx which would make it much clearer which variable has which role.
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