Index exceeds the number of array elements (2). Error (line 41)

Question

camilo jose 2020-10-21

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/620698-index-exceeds-the-number-of-array-elements-2-error-line-41

编辑： per isakson 2020-10-21

I don't understand this error, I get this Index exceeds the number of array elements (2). Error (line 41) Can you please correct this problem for me?

Index exceeds the number of array elements (2).
Error in Untitled (line 35)
       B(i) = 3*(dy_v(i) - (1/h_v(i-1))*(y_v(i) - y_v(i-1)) );       

%% Enter the data for the curve-1 
clear    % Clear all the previous Variables 
syms x  % Define x as a symbolic variable 
x_v=[27.7 28 29 30];  % The corresponding x values 
y_v = [4.1 4.3 4.1 3.0];    % The corresponding y values 
dy_v= [0.33 -1.5];  % The slopes/clamps at the end. The mid values are filled with NaN values 
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