What is the problem for the following code?

Question

PULAK Kumer 2020-11-27

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/664353-what-is-the-problem-for-the-following-code

关闭： MATLAB Answer Bot 2021-8-20

clc; clear all; close all;
fprintf('\n************************************************************');
fprintf('\n*** Interpolation by Newtons Forward Difference Formula  *'); fprintf('\n************************************************************'); n = input('\nEnter number of data points = '); h = input('\nEnter step size (h) = ') x(1) = input('\nx0 = '); y(1) = input('y0 = '); for i=2:n x(i)=x(i-1)+h; fprintf('\nX%d = %f',i,x(i)); fprintf('\t\tY%d: ',i); y(i) = input(''); end x_reqd = input('\nEnter X for which value of Y is sought: '); s=(x_reqd-x(1))/h; for i=1:n diff(i,1)=y(i); end %% Calculate Forward Differance Table for j=2:n for i=1:n-j+1 diff(i,j)=diff(i+1,j-1)-diff(i,j-1); end end fprintf('\n\t Forward Differance Table');
%% Print Forward Differance Table offset=1; for i=0:n*2-2 index=floor(i/2); fprintf("\t\t") if mod(i,2)==0 fprintf('\n %.6f',x(index+offset)); end if n>i j_max=i else j_max=n*2-i-1 end
    for j=0:j_max
        if mod(i,2)==mod(j,2)
        fprintf('\t\t%.6f',diff(index-j/2+offset,j+offset));
        end
    end
end

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Answer 1

Walter Roberson 2020-11-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/664353-what-is-the-problem-for-the-following-code#answer_557318

在 MATLAB Online 中打开

h = input('\nEnter step size (h) = ') x(1) = input('\nx0 = ');

You need a comma or a semi-colon between those two commands.

Better yet would be to format your code with one command per line. Whitespace is free, but the cost of a human trying to figure out what your run-on code does is not free.

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PULAK Kumer 2020-11-27

在 MATLAB Online 中打开

clc; 
clear all;
close all;
fprintf('\n************************************************************');
fprintf('\n*** Interpolation by Newtons Forward Difference Formula  *'); 
fprintf('\n************************************************************'); 
n = input('\nEnter number of data points = '); h = input('\nEnter step size (h) = ');
x(1) = input('\nx0 = ');
y(1) = input('y0 = '); 
for i=2:n 
    x(i)=x(i-1)+h; 
    fprintf('\nX%d = %f',i,x(i)); 
    fprintf('\t\tY%d: ',i); 
    y(i) = input(''); 
end
x_reqd = input('\nEnter X for which value of Y is sought: ');
s=(x_reqd-x(1))/h; 
for i=1:n 
    diff(i,1)=y(i); 
end
%% Calculate Forward Differance Table 
for j=2:n 
    for i=1:n-j+1 
        diff(i,j)=diff(i+1,j-1)-diff(i,j-1); 
    end 
end 
fprintf('\n\t Forward Differance Table');
%% Print Forward Differance Table
offset=1; 
for i=0:n*2-2 
    index=floor(i/2); 
    fprintf("\t\t") 
    if mod(i,2)==0 
        fprintf('\n %.6f',x(index+offset));
    end
    if n>i 
        j_max=i; 
    else 
        j_max=n*2-i-1;
    end
    for j=0:j_max
        if mod(i,2)==mod(j,2)
        fprintf('\t\t%.6f',diff(index-j/2+offset,j+offset));
        end
    end
end

Show that :

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Error in kkkuntitled (line 43)

fprintf('\t\t%.6f',diff(index-j/2+offset,j+offset));

what can i do now?

Walter Roberson 2020-11-27

在 MATLAB Online 中打开

Change

fprintf('\t\t%.6f',diff(index-j/2+offset,j+offset));

to

fprintf('\t\t%.6f',diff(index-floor(j/2)+offset,j+offset));

Walter Roberson 2020-11-27

By the way, my belief is that the original C code had bugs.

Difficult to be sure, though, due to the lack of documentation... it is always possible that it had strange design requirements and was manually optimized to fit those requirements, and so only looks like it has mistake piled on mistake.