symbolic expression to function

The following code is to obtain a formula of calculating the determinant of the symmetric matrix.

function [ yy ] = detF( xdm )

ni = (1 + xdm) * xdm /2;
xx = sym('xx', [ni,1]);
xM = sym('xM', [xdm,xdm]);
for i = 1:xdm
    ia = i * (i-1) /2 +1;
    ib = i + ia - 1;
    xM(i, 1:i) = xx(ia : ib);
end

for j = 1:xdm-1
    for k = j+1:xdm
        xM(j,k) = xM(k,j);
    end
end

y = det(xM);

yy = symfun(y,xx);

end

xdm is the demension of the matrix. You can test the code by 'detF(2)'. The code returns something like

yy(xx1, xx2, xx3) = - xx2^2 + xx1*xx3

However, the argument of the symfun is 3 elements, what I need is a vector input like yy(x) = -x(2)^2 + x(1)*x(3)

Any suggestion? Thank you in advance.

Qun

Answer 1

[Walter Roberson]

Use matlabFunction with the 'vars' option and pass {xx} as the value of the option, or possibly the transpose of that depending if you want row vectors or column vectors. To emphasize, for this situation you need to pass a cell array that contains a symbolic vector

[Qun Wu]

Thank you for your reply. I tried matlabFunction and pass xx as the 'var' value. And I got @(xx1,xx2,xx3)xx1.*xx3-xx2.^2 which is not the required one. I need something like @(x) x(1)*x(3) - x(2)^2

[Walter Roberson]

yy = matlabFunction(y, 'vars', {xx})

Notice the {}