MATLAB: Evaluate Sym values

convertdoublesym

Hi, I trying to make a simple program, I would like to know how to make this

syms x; fun=x^2; x0=2;

x=x0; fun

And what a expect in the last line is 4 but I get X^2 How can I convert the sym to a double, I tried with doble(fun).

thank you

Best Answer

syms x;
fun=x^2;
x0=2;
subs(fun,x,x0)
double(ans)

Related Solutions

MATLAB: Symbolic differentiation with fminunc


function [f,g] = rosenbrockwithgrad_s(x)
X = sym('x', [1 2]);
% Calculate objective f

F = 100*(X(2) - X(1)^2)^2 + (1-X(1))^2;
f = double( subs(F, X, x) );
if nargout > 1 % gradient required
   G = diff(F);
   g = double( subs(G, X, x) );
end

However, this would involve repeated calculation of diff(F) symbolically, which is pointless. Instead you would do something like,

    function [f, g] = f_and_g(x, F, G)
        f = F(x);
        if nargout > 1
            g = G(x);
        end
    end

together with (outside)

X = sym('x', [1 2]);
% Calculate objective f
f = 100*(X(2) - X(1)^2)^2 + (1-X(1))^2;
g = diff(f);
F = matlabFunction(f, 'vars', {X});
G = matlabFunction(g, 'vars', {X});
x = fminunc( @(x) f_and_g(x, F, G), x0 )

MATLAB: Doesn’t the code work correctly

Because you mixed function handle in place of subs()/matlabFunction().

Try this:

syms x1 x2 
F=x1^2+x2^2-4*x1-2*x1*x2;
gradx1=gradient(F,x1); 
gradx2=gradient(F,x2);
c=[gradx1; gradx2];
fun_x0= F;
fun_c1_x0=gradx1
fun_c2_x0=gradx2 
x0=[1,1];
c_x0_1=subs(fun_c1_x0,{x1,x2},{x0(1),x0(2)});
c_x0_2=subs(fun_c2_x0,{x1,x2},{x0(1),x0(2)});
c0=[c_x0_1; c_x0_2];
c0=c0.'

Best Answer

Related Solutions

MATLAB: Symbolic differentiation with fminunc

MATLAB: Doesn’t the code work correctly

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