Index exceeds the number of array elements (4)

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camilo jose
camilo jose 2020-10-20
评论： camilo jose 2020-10-20
I am computing and I get an error on line 38
x_v=[1 2 5 6 7 8 10 13 17]; % The corresponding x values
y_v = [3 3.7 3.9 4.2 5.7 6.6 7.7 6.7 4.5]; % The corresponding y values
dy_v= [1 NaN NaN -0.67]; % The slopes/clamps at the end
n=length(x_v) -1; % Find the n for size of the matrix
h_v = diff(x_v); % Find the h values (step size) from x values
%% Create Matrix A
for i=1:n+1 % Start row loop
for j=1:n+1 % Start column loop
if i==1&&j==1 % Condition for first row and first column
A(i,j) = 2*h_v(i); % First Entry
elseif i==n+1&&j==n+1 % Condition for last row and last column
A(i,j) = 2*h_v(i-1); % Last Entry
elseif j==i-1 % Condition for element jsut left of the diagonal
A(i,j) = h_v(i-1);
elseif j==i+1 % Condition for element jsut right of the diagonal
A(i,j) = h_v(i);
elseif i==j % Condition for element in diagonal
A(i,j) = 2*(h_v(i-1)+h_v(i));
else
A(i,j) = 0; % Condition for all other elements in matrix
end
end
end
%% Create Vector B
for i=1:n+1
if i==1 % Condition for first row
B(i) = 3*((1/h_v(i))*(y_v(i+1) - y_v(i)) - dy_v(i));
elseif i==n+1 % Condition for last row
B(i) = 3*(dy_v(i) - (1/h_v(i-1))*(y_v(i) - y_v(i-1)) );
else % Condition for all other elements
B(i) = 3*((1/h_v(i))*(y_v(i+1) - y_v(i)) - (1/h_v(i-1))*(y_v(i) - y_v(i-1)));
end
end
%% Find the Matrix C
c = (A^-1)*B'; % Find the product of inverse of A and B
for i=1:n % Loop for remaining constants (bs) and (ds)
b(i) = (1/h_v(i))*(y_v(i+1) - y_v(i)) - (h_v(i)/3)*(2*c(i) + c(i+1));
d(i) = (1/(3*h_v(i)))*(c(i+1) - c(i));
end
%% Find the splines
for i=1:n
S{i} = num2str(y_v(i),8) + num2str(b(i),8)*(x- num2str(x_v(i),8) ) + num2str(c(i),8)*(x- num2str(x_v(i),8)).^2 + num2str(d(i),8)*(x- num2str(x_v(i),8)).^3;
SS{i} =['$$' latex(S{i}) '$$'];
SS2{i} =[ latex(S{i}) ];
SSD{i} =[ latex(diff(S{i})) ];
end

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采纳的回答

Walter Roberson
Walter Roberson 2020-10-20
dy_v= [1 NaN NaN -0.67]; % The slopes/clamps at the end
4 entries.
x_v=[1 2 5 6 7 8 10 13 17]; % The corresponding x values
n=length(x_v) -1; % Find the n for size of the matrix
So n is 9-1 = 8
%% Create Vector B
for i=1:n+1
So i can be at most 8+1 = 9
if i==1 % Condition for first row
B(i) = 3*((1/h_v(i))*(y_v(i+1) - y_v(i)) - dy_v(i));
elseif i==n+1 % Condition for last row
B(i) = 3*(dy_v(i) - (1/h_v(i-1))*(y_v(i) - y_v(i-1)) );
else % Condition for all other elements
B(i) = 3*((1/h_v(i))*(y_v(i+1) - y_v(i)) - (1/h_v(i-1))*(y_v(i) - y_v(i-1)));
end
When i reaches 5, it is not the special case i==1 or the special case i==n+1, so the else branch is used. But the else branch does not reference dy_v(i) so that is not a problem.
But when i reaches n+1 the elseif branch is taken, and dy_v(i) is referenced, which is a problem because i = 9 and dy_v(9) does not exist.
You could change the code to
if i==1 % Condition for first row
B(i) = 3*((1/h_v(i))*(y_v(i+1) - y_v(i)) - dy_v(1));
elseif i==n+1 % Condition for last row
B(i) = 3*(dy_v(end) - (1/h_v(i-1))*(y_v(i) - y_v(i-1)) );
else % Condition for all other elements
B(i) = 3*((1/h_v(i))*(y_v(i+1) - y_v(i)) - (1/h_v(i-1))*(y_v(i) - y_v(i-1)));
end
but then I would have to ask why you have more than two entries in dy_v since you only reference the first and last of them?
  2 个评论
camilo jose
camilo jose 2020-10-20
Thanks!
Now I have problem near line 65
for i=1:n
S{i} = num2str(y_v(i),8) + num2str(b(i),8)*(x- num2str(x_v(i),8) ) + num2str(c(i),8)*(x- num2str(x_v(i),8)).^2 + num2str(d(i),8)*(x- num2str(x_v(i),8)).^3;
SS{i} =['$$' latex(S{i}) '$$'];
SS2{i} =[ latex(S{i}) ];
SSD{i} =[ latex(diff(S{i})) ];
end

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