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Index exceeds the number of array elements

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Naman Singh
Naman Singh on 25 Nov 2020
Commented: VBBV on 25 Nov 2020
function [x, y1, y2, y3, y4 ] = FDEx4_1(N,kn,F)
clc
mm = 4;
N = 200;
h = 1/N;% mesh size
kn = 0.5;%Reynolds number
F = 0.23;
x = (0:h:1)'; % nodes
M = zeros(mm*(N+1),mm*(N+1));
b = zeros(mm*(N+1),1);
Done = 0;
Max_iter = 10;
y0 = zeros(mm*(N+1),1);
for i = 1:N+1
y0(mm*(i-1)+1) = 0;
y0(mm*(i-1)+2) = 0;
y0(mm*(i-1)+3) = 0;
y0(mm*(i-1)+4) = 0;
end
y1 = zeros(N+1,1);
y2 = zeros(N+1,1);
y3 = zeros(N+1,1);
y4 = zeros(N+1,1);
for i = 1:N+1
y1(i) = x(mm*(i-1)+1);
y2(i) = x(mm*(i-1)+2);
y3(i) = x(mm*(i-1)+3);
y4(i) = x(mm*(i-1)+4);
end
iter = 0;
while (~Done)
for i = 1:N
xip1 = 0.5*(x(i)+x(i+1));
yip1 = 0.5*(y0(mm*(i-1)+1:mm*i)+y0(mm*i+1:mm*(i+1)));
Aip1= [0,-1./kn, 0, 0;
0, 0, -F./(yip1(3)).^2, 0;
0, 0, 0, -4./(15*kn);
0, (2*yip1(2))./(kn), 0, 0];
Qip1 = [-(yip1(2))./kn; F./yip1(3); (4*yip1(4))./(15*kn); ((yip1(2)).^2)./kn];
fip1 = Qip1-Aip1*yip1;
M(mm*(i-1)+1:mm*i,mm*(i-1)+1:mm*i) = -(0.5*Aip1+eye(mm)/h);
M(mm*(i-1)+1:mm*i,mm*i+1:mm*(i+1)) = (-0.5*Aip1+eye(mm)/h);
b(mm*(i-1)+1:mm*i) = fip1;
end
Ba = [sqrt(2./pi*y3(0)), 1, -(y1(0))*(1./sqrt(pi*2)*(y3(0).^1.5)), 0;
0, 0, 0, 0;
0, 0, (sqrt(2)*(1./(y3(0)).^1.5)*sqrt(pi))*(y3(0) + 1), 1;
0, 0, 0, 0];
Bb = [0, 0, 0, 0;
-sqrt(2./(pi*y3(1))), 1, y1(1)*(1./(y3(0)).^1.5*sqrt(2*pi)), 0;
0, 0, 0, 0;
0, 0, -(sqrt(2)*(1./(y3(0)).^1.5)*sqrt(pi))*(y3(1) + 1), 1];
M(mm*((N+1)-1)+1:mm*(N+1),mm*((N+1)-1)+1:mm*(N+1)) = Bb;
M(mm*((N+1)-1)+1:mm*(N+1),1:mm) = Ba;
alpha = [0; 0; 0; 0];
b(mm*((N+1)-1)+1:mm*(N+1)) = alpha;
x = M\b;
error = max(abs(x-y0));% max |y_i-y_i^*|
iter = iter+1;
disp(['Error in step ',num2str(iter),' is : ',num2str(error)])
y0 = x;
Done = (iter>=Max_iter)||(error<0.000001);
end
It says
Index exceeds the number of array elements (201).
Error in FDEx4_1 (line 31)
y2(i) = x(mm*(i-1)+2);
How do i fix this?

  1 Comment

per isakson
per isakson on 25 Nov 2020
Write some comments, which explains what the loops are intended to achieve.

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Accepted Answer

VBBV
VBBV on 25 Nov 2020
%if true
x = 0:h:1;% size has 201 elements
Define this according to function calculations e.g.
x = 0:1/((N+1)*mm):1;% size of 805

  4 Comments

Show 1 older comment
VBBV
VBBV on 25 Nov 2020
Matlab does not use zero or decimal indexing for matrix definitions. Since y1 and y3 are matrices using 0 as index which is undefined in matlab, it produces error.
You can set it to y1(1) or y3(1) if you want to use only first element of those matrix
VBBV
VBBV on 25 Nov 2020
in the same function you are also trying to calculate x vector using the matrix inversion operator \
VBBV
VBBV on 25 Nov 2020
Also an end statement for the function is required

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