清空筛选条件
清空筛选条件

double integral using trapz

6 次查看（过去 30 天）
ray sanchez
ray sanchez 2015-5-18
评论： ray sanchez 2015-5-19
I'm trying to approximate a double integral using traps. This code is telling me the answer is 0 when it should be pi/4. I'm not sure how to fix it.
clear; close all; clc;
x = 0:.1:1;
y = 0:.1:sqrt(1-x.^2);
[X,Y] = meshgrid(x,y);
F = 1;
I = trapz(x,trapz(y,F));

请先登录，再回答此问题。

回答（2 个）

Walter Roberson
Walter Roberson 2015-5-18
0:.1:sqrt(1-x.^2) with x a vector, tries to use a vector as the termination value for the iteration. When the termination value is a vector, only the first element of the vector is used. Your y is thus the same as
0:.1:sqrt(1-x(1).^2)
and your x and y are both linear -- actually they are even the same. Nothing much to integrate.
  3 个评论
显示 1更早的评论
Walter Roberson
Walter Roberson 2015-5-18
You are still trying to use a vector in the last position of the colon operator ':'. That is not going to work.
I suggest you do this:
x = 0:0.1:1;
y = 0:0.1:1;
[X,Y] = meshgrid(x,y);
F = @(x,y) 1;
Z = F(X,Y);
Z(Y > sqrt(1-X.^2)) = 0;
And now you can use this File Exchange Contribution
ray sanchez
ray sanchez 2015-5-19
I'm not sure how to use that file. Do I have this on a script and use the file as a function on another script? Sorry I'm really new to this stuff.

请先登录，再进行评论。

Andrei Bobrov
Andrei Bobrov 2015-5-18
Try use idea by Walter (+1):
x = 0:.1:1;
f = @(x)sqrt(1 - x.^2);
[yy,xx] = ndgrid(x);
out = trapz(x,trapz(yy,f(xx)>=yy),2);

类别

在 Help Center 和 File Exchange 中查找有关 Numerical Integration and Differentiation 的更多信息

标签

产品

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by