I need help as soon as possible

Question

Mahdi Almahuzi 2020-3-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513036-i-need-help-as-soon-as-possible

编辑： Walter Roberson 2020-3-26

i write this code it says there is error in line 17 how to solve it ?

clc
clear
close all
N=10;
a=0;b=2;alp=0.5;
f=@(t,y)y-t^2+1;
yexact=@(y,t)(1+t)^2-0.5*exp(t);
h=(b-a)/N;
w=[alp];
i=1;
t=a:h:b;
for i=1:N
    w(i+1)=w(i)+h*f(t(i),w(i));
    i=i+1;
    
end
error=abs(yexact-w);       %here is the error 
w;
disp('-------------------------------------------------');
disp('t      EXACT          NUMERICAL         ERROR');
disp('-------------------------------------------------');
fprintf("%3.0f     %6.2f     %5.6f        %5.6f \n",N,yexact,w,error);     %and here also 

6 个评论
显示 4更早的评论隐藏 4更早的评论

darova 2020-3-26

please see this: function_handle

Adam 2020-3-26

For future reference, question titles like 'I need help as soon as possible' or 'Urgent...' just annoy people and are actually less likely to get you fast help than just giving a question title that says what your question is about. If people can help they will, but telling people your question is somehow more urgent than everyone else's will sometimes just cause people to ignore it.

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Answer 1

Stephan 2020-3-26

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513036-i-need-help-as-soon-as-possible#answer_422070

在 MATLAB Online 中打开

Try to work with a table to make life easier:

N=1:10;
a=0;b=2;alp=0.5;
f=@(t,y)y-t^2+1;
yexact=@(y,t)(1+t).^2-0.5*exp(t);
h=(b-a)/N(end);
w=alp;
t=a:h:b;
for i=N
    w(i+1)=w(i)+h*f(t(i),w(i));
    i=i+1;
    
end
error=yexact(w,t)-w;
yexact_vals = yexact(w,t)';
result = table(t(:), yexact_vals, w(:), error(:),'VariableNames',...
    {'t','EXACT','NUMERICAL','ERROR'})

results in:

result =
  11×4 table
     t     EXACT     NUMERICAL     ERROR  
    ___    ______    _________    ________
     0.5        0.5             0
2    0.8293        0.8      0.029299
4    1.2141      1.152      0.062088
6    1.6489     1.5504      0.098541
8    2.1272     1.9885       0.13875
  2.6409     2.4582       0.18268
2    3.1799     2.9498       0.23013
4    3.7324     3.4518       0.28063
6    4.2835     3.9501       0.33336
8    4.8152     4.4282       0.38702
  5.3055     4.8658       0.43969