Question

我正在尝试解决一个双积分，我用quadgk函数解决内部和外部积分。

% The integrand is of course a function of both x and y
integrand = @(x,y) (phi(j,y,X) - phi(j,x,X))*(phi(i,y,X) - phi(i,x,X))/abs(y-x)^(2*s+1)

% The inner integral is a function of x, and integrates over y
inner = @(x) quadgk(@(y)integrand(x,y), x-lambda, x+lambda)

% The inner integral is integrated over x to yield the value of the double integral 
dblIntegral = quadgk(inner, -(1+lambda), 1+lambda)

我收到以下错误：

integrand = @(x,y)(phi(j,y,X)-phi(j,x,X))*(phi(i,y,X)-phi(i,x,X))/abs(y-x)^(2*s+1)
inner = @(x)quadgk(@(y)integrand(x,y),x-lambda,x+lambda)

??? Error using ==> quadgk at 108
A and B must be scalar floats.

Error in ==> @(x)quadgk(@(y)integrand(x,y),x-lambda,x+lambda)
Error in ==> quadgk>evalFun at 344
        fx = FUN(x);

Error in ==> quadgk>f1 at 362
    [y,too_close] = evalFun(tt);

Error in ==> quadgk>vadapt at 258
        [fx,too_close] = f(x);

Error in ==> quadgk at 197
[q,errbnd] = vadapt(@f1,interval);

Error in ==> frational_laplacian at 29
dblIntegral = quadgk(inner, -(1+lambda), 1+lambda)

Answer 1

您遇到了这个问题，因为内部quadgk使用值向量计算传递的函数。这意味着在行

dblIntegral = quadgk(inner, -(1+lambda), 1+lambda)

正在调用函数inner，x是向量。 quadgk要求a和b（在本例中为x±lambda）为标量，因此您会得到您所看到的错误。如果您想确保inner总是以标量作为输入，您可以使用

dblIntegral = quadgk(@(x)arrayfun(inner,x), -(1+lambda), 1+lambda)

如何在matlab中使用quadgk函数作为函数句柄？

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