Use quadgk with multiple Inputs with Matlab Coder

Question

Antonia Lichtenegger 2014-2-17

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/116449-use-quadgk-with-multiple-inputs-with-matlab-coder

评论： Tunga Rangaswamy 2019-10-16

Hi I want to create a C file out of my Matlab file. In my Matab file I have to make some integrations, that is way I am using the quadgk function. My problem is now, that the Matlab Coder for generating the C Code doesn't allow function handels.

I want to integrate the function

function val=integrand1(x,c,d) val=x*c+d; end

by the follwing term

Integral = quadgk('integrand1',z(1),z(2),-1,z(2))

So the intergal goes from z(1) to z(2) and for the parameters c and d I want to use the values -1 and z(2). If I do so the Matlab Coder gives the errow ??? First input argument must be a function handle.

But how can I use quadgk instead? Thank you very much for any help.

Best regards Antonia

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Mike Hosea 2014-2-20

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/116449-use-quadgk-with-multiple-inputs-with-matlab-coder#answer_124990

编辑：Mike Hosea 2014-2-20

在 MATLAB Online 中打开

I don't have a lot of time to type this. Hopefully if it isn't clear I can come back and add some detail.

The way we normally do this in MATLAB is not with a string to represent the integrand. That is obsolete. The standard way would be integrate the anonymous function @(x)integrand1(x,c,d), where c and d would be defined before, e.g.

quadgk(@(x)integrand1(x,-1,z(2)),z(1),z(2))

Unfortunately, this won't work in MATLAB Coder because MATLAB Coder doesn't support anonymous functions. So you will have to do something a little more complicated using persistent variables, something like

function val = integrand(x,c,d)
persistent c_saved,d_saved
if isempty(c_saved)
    c_saved = 0;
    d_saved = 0;
end
if nargin >= 2
    c_saved = c;
end
if nargin >= 3
    d_saved = d;
end
val = x*c_saved + d_saved;

Then to use it, you just call it first with your desired c and d.

integrand1(0,-1,z(2));
integral = quadgk(@integrand1,z(1),z(2));

I apologize if I have made a typo or some other boneheaded error above. I don't have time to test it, but we test QUADGK for code generation using this basic approach, so I know it can work. -- Mike

5 个评论
显示 3更早的评论隐藏 3更早的评论

Tunga Rangaswamy 2019-10-16

编辑：Tunga Rangaswamy 2019-10-16

Hi Mike,

Thanks for your answer on using anonymous functions for Matlab coder. It is very helpful.

I am following the same technique for bisection method. Let's say the function equation has an equation to be solved using bisection method. I have modified the function example using persistent variables. I would expect the code to evaluate the equation with values starting from a (first approx.) and b (second approx.) and intermediate values determined by the bisection function to find the zero crossing or the root. Instead the code throws an error Undefined function or variable 'x'.

NOTE: Expected answer = - 5

Can you please help me with this?

%**********************main script**************************%

% with function handle

fun = @(x) equation(x,8,15);

root = bisection(fun,-10,-4,1e-03);

% without using funtion handle which gives the error

% equation(x,8,15);

% root = bisection(@equation,-10,-4,1e-03);

%**********************equation**************************%

function fun = equation(x,a,b)

persistent a_val

persistent b_val

if isempty(a_val)

a_val = 0;

b_val = 0;

end

if nargin >= 2

a_val = a;

end

if nargin >= 3

b_val = b;

end

fun = x^2 + a_val*x + b_val;

end

%*******************bisection method*********************%

function y = bisection(f,a,b,tol)

y = (a + b)/2;

err = abs(f(y));

while err > tol

if f(a)*f(y)<0

b = y;

else

a = y;

end

y = (a + b)/2;

err = abs(f(y));

end

Steven Lord 2019-10-16

This isn't really related to the original question. You should ask it as a separate question rather than as a comment to the accepted answer of a question that's more than 5 years old.

Tunga Rangaswamy 2019-10-16

Thanks Steven!

My question is also based on anonymous function and MATLAB coder which seemed aligned to the previous question. However, I have asked this a separate question now and I am looking forward to an answer.

请先登录，再进行评论。

Use quadgk with multiple Inputs with Matlab Coder

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

5 个评论
显示 3更早的评论隐藏 3更早的评论

更多回答（0 个）

另请参阅

类别

标签

产品

Community Treasure Hunt

Use quadgk with multiple Inputs with Matlab Coder

0 个评论 显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

5 个评论 显示 3更早的评论隐藏 3更早的评论

更多回答（0 个）

另请参阅

类别

标签

产品

Community Treasure Hunt

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

5 个评论
显示 3更早的评论隐藏 3更早的评论