An implementation issue with MatlabFunction

Hello,

I have a question which I explain by an example.

function ll = LL(X1,X2,X01,X02,par1,par2,par3,par4,par5,par6)

THE BODY WILL BE EXPLAINED LATER

end

PLEASE NOTE THAT MY ACTUAL PROBLEM IS MORE COMPLICATED THAN THIS. SO, PLEASE GIVE ME GENERAL ADVICES RATHER THAN A SPECIFIC ONES WHICH PROBABLY WORK FOR THIS PROBLEM ONLY. THANKS!

This function is created by the followig commands

syms x y

syms X X0 [1 2]

syms par [1 6]

mu1(x,y)=[par(1)*x^2*y+par(2)*y^3+x^3;par(3)*x^5*y^7+par(4)*y];sigma1(x,y)=[par(5)+x*y -x;y^2*x x*y*par(6)];

V=argnames(mu1);

p=sym2cell(X0);

mu_X0=subs(mu1,V,X0).';mu_X0=mu_X0(p{:});

sigma_X0=subs(sigma1,V,X0);sigma_X0=sigma_X0(p{:});

D=sigma_X0*sigma_X0.'; det_D=simplify(det(D)); inv_D=simplify(inv(D));

dt=1;S=1/dt*(X-X0-mu_X0*dt)*inv_D*(X-X0-mu_X0*dt).';

d=2;LL=-1/2*(d*log(2*pi*dt)+log(det_D)+S);

LL=matlabFunction(LL,'File','LL','vars',[X X0 par],'Outputs',{'ll'}); %Log-Likelihood

My question: I wouldlike to make a slight change to the way this matlabfunction is created so that at the end it would look like the following

function ll = LL(X,X0,par1,par2,par3,par4,par5,par6)

BODY: here, instead of stuff like X1,X2,X01,X02 I would like to have stuff like X(1),X(2),X0(1),X0(2)

end

I find it difficult to implement this (and this is very annoying).

I look forward to your kind help!

Thanks,

Babak

Answer 1

[Star Strider]

If you want matlabFunction to produce a vector for several arguments, in the 'Vars' argument, enclose them in square brackets to concatenate them.

Example —

syms a b x1 x2 x3 
f = a*x1 + b*x2 + x3

f = 

F = matlabFunction(f, 'Vars',{a,b,[x1,x2,x3]})

F = function_handle with value:
    @(a,b,in3)in3(:,3)+a.*in3(:,1)+b.*in3(:,2)

.

The ‘x’ arguments will appear as a row vector of ‘in3(1)’, ‘in3(2)’ and ‘in3(3)’ however when you call the function, you can of course name the arguments anything you want. Also, the arguments in the square brackets can be any arguments you want, including all of them. They do not have to be any specific subset.

This is a general illustration, however it will work for any function you choose as a function argument to matlabFunction.

.

EDIT — Corrected typographical errors.

.

[Mohammad Shojaei Arani]

Hi Star,

That was exactly what I needed.

Thanks VERY much!

Babak

[Star Strider]

As always, my pleasure!

[Walter Roberson]

This is the advice I gave you in https://www.mathworks.com/matlabcentral/answers/1884182-a-symbolic-implementation-issue#answer_1136137 along with an explanation for why you were having difficulty.

[Mohammad Shojaei Arani]

Hi Walter,

I looked at it again. Indeed, a nice and comprehensive answer. You are right. Sorry (I do not remember, but probably I did not understand it then). I admit that I understand math very well but when it comes to programming ...sometimes I really want to punch the screen :-)