MATLAB: How to convert into double

convertdoubleSymbolic Math Toolbox

Hello,
I wrote the following code:
tfail = [5571.760,5573.742,5654.457,6079.693,6081.927,6172.915,6515.064,6517.515,6617.308,7095.558,7098.298,7209.831,7530.929,7533.885,7654.224,7966.300,7969.472,8098.617,8401.671,8405.059,8543.009,8982.166,8985.843,9135.533,9852.908,9857.017,10024.38,10868.774,10873.387,11061.234];
n=length(tfail);
beta_hat = 4.2915822; 
B_hat = 1861.6186657; 
C_hat = 58.9848692;
syms t B beta C
y(t) = (exp(-B/((heaviside(t)-heaviside(t-2000))*(330)+(heaviside(t-2000)-heaviside(t-3000))*(350)+...
    (heaviside(t-3000)-heaviside(t-14000))*(390))))/C;
ogL=0;
for i=1:n 
    tfail(i);
    I(i) = int(y(t),t,0,tfail(i));
    y_new(i)=subs(y,t,tfail(i));
    logL =logL+log((beta*y_new(i)*(I(i))^(beta-1))*exp(-((I(i))^beta)));
end
p = int(y(t),t,0,14000);
u = beta*log(p);
du_dB = diff(u,B);
du_dbeta = diff(u,beta);
du_dC = diff(u,C);
du_dB_sub = subs(du_dB,{beta,B,C},{beta_hat,B_hat,C_hat});
du_dbeta_sub = subs(du_dbeta,{B,C},{B_hat,C_hat});
du_dC_sub = subs(du_dC,{beta,B,C},{beta_hat,B_hat,C_hat});
v=[beta;B;C]; 
H=hessian(logL,v); 
H_negatv=-1*H;
now I would like to calculate the inverse of H_negatv by using:
H_inverse=inv(H_negatv);
But that doesn´t work. So I tried out:
h = 1\H_negatv.
That´s good so far.
But now I would do sth. like that:
w=subs(h,[beta,B,C],[beta_hat,B_hat,C_hat]);
F_direct = w;
In according to calculate:
Var_B_hat_direct = double(F_direct(2,2));
But I can´t do that in MATLAB.
Does somebody have an idea how to solve that problem?

Best Answer

Working notes for me.
rational = @(V) sym(V, 'r');
if ismember( exist('hessian'), [2, 3, 5, 6, 8])   %is it an executable function?
  Hess = @(M,V) hessian(M,V)
else
  Hess = @(M,V) maple('Student[VectorCalculus][Hessian]', M, maple('convert', V, 'list'));
end
tfail = rational([5571.760, 5573.742, 5654.457, 6079.693, 6081.927, 6172.915, 6515.064, 6517.515, 6617.308, 7095.558, 7098.298, 7209.831, 7530.929, 7533.885, 7654.224, 7966.300, 7969.472, 8098.617, 8401.671, 8405.059, 8543.009, 8982.166, 8985.843, 9135.533, 9852.908, 9857.017, 10024.38, 10868.774, 10873.387, 11061.234]);
n = length(tfail);
beta_hat = rational(4.2915822); 
B_hat = rational(1861.6186657); 
C_hat = rational(58.9848692);
syms t B beta C
y = (exp(-B/((heaviside(t) - heaviside(t-2000)) * (330) + (heaviside(t-2000) - heaviside(t-3000)) * (350) + (heaviside(t-3000) - heaviside(t-14000)) * (390))))/C;
Z = rational(0);
LogL = Z;
I = rational(zeros(1,n));
y_new = rational(zeros(1,n));
new_term = rational(zeros(1,n));
for i = 1:n 
    I(i) = simplify( int(y, t, Z, tfail(i)) );
    y_new(i) = simplify( subs(y, t, tfail(i)) );
    new_term(i) = log((beta * y_new(i) * (I(i))^(beta-1)) * exp(-((I(i))^beta)));
    logL = logL + new_term(i);
end
p = int(y, t, Z, rational(14000));
u = beta * log(p);
du_dB = diff(u, B);
du_dbeta = diff(u, beta);
du_dC = diff(u, C);
du_dB_sub = subs(du_dB, {beta, B, C}, {beta_hat, B_hat, C_hat});
du_dbeta_sub = subs(du_dbeta, {B,C}, {B_hat,C_hat});
du_dC_sub = subs(du_dC, {beta,B,C}, {beta_hat,B_hat,C_hat});
v = [beta; B; C]; 
H = Hess(logL, v);
%the next will probably fail, running out of memory
Hs = simplify(H);
H_negatv = -1*Hs;
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