How can I get the plot correctly?

Hello,

I write some code like this:

vx = 30:10:300;
vy = 2:0.04:3;
[xx,yy] = meshgrid(vx,vy);
zz = get_critical_value(yy,xx,0.05);
surf(xx,yy,zz)

Unfortunately, Matlab returns some feedback messages below:

======================================================

FZERO cannot continue because user-supplied function_handle ==>
@(czero)integral(@(y)fun(y,czero),0,3*Cp*sqrt(n))-alpha failed with the error below.

   Inner matrix dimensions must agree.

Error in get_critical_value (line 15)
    czero_sol = fzero(@(czero) integral(@(y)fun(y,czero),0,3*Cp*sqrt(n))-alpha,czero_guess);

======================================================

What's wrong with my program? How can I solve this situation to get the right plot? Thanks!

*The code of get_critical_value:

    function czero_sol = get_critical_value(C,n,alpha)
     if n<100
        Cp = C+0.33;
     else
        Cp = C+0.12;
     end
     fun = @(y,czero)chi2cdf((n-1)*(3*Cp*sqrt(n)-y).^2/(9*n*czero^2),n-1).*(normpdf(y+3*(Cp-C)*sqrt(n))+normpdf(y-3*(Cp-C)*sqrt(n)));
     czero_guess = 1;
     czero_sol = fzero(@(czero) integral(@(y)fun(y,czero),0,3*Cp*sqrt(n))-alpha,czero_guess);
    end

Answer 1

[Robert]

Your function get_critical_value is not build to handle array inputs. It is always nice if you can vectorize your function to take advantage of MATLAB's fast array operations but in your case, integral and fzero will make this difficult.

Instead of vectorizing, you could perform the operation one-at-a-time using arrayfun

vx = 30:10:300;
vy = 2:0.04:3;
[xx, yy] = meshgrid(vx, vy);
zz = arrayfun(@(y, x) get_critical_value(y, x, 0.05), yy, xx);
surf(xx, yy, zz)

[Louis Liu]

Thanks! But I think I have to study arrayfun() first. It's my first time to know this function. Hope I could truly understand whole your answer...