About Matrix F

[qqstar-423]

F = jacobian_state(X, dt);
In function jacobian_state writes that

double delta=0.0001;
for(;;){
x_plus = x;
x_plus(i) = x_plus(i) + delta; 
.......
}

When f () calculates the partial derivative of x, why should we set delta to 0.0001? Will it get better results if we set delta smaller?

[gilmarpcjunior]

F = jacobian_state(X, dt); In function jacobian_state writes that

double delta=0.0001;
for(;;){
x_plus = x;
x_plus(i) = x_plus(i) + delta; 
.......
}

When f () calculates the partial derivative of x, why should we set delta to 0.0001? Will it get better results if we set delta smaller?

The delta variable is the time interval to calculate the Jacobian matrix. Normally you can use 1e-9, but it's not a rule. I set the value 0.0001 arbitrarily, but I performed some experiments changing this value. This value cannot be too high or too low because it will not express the differentiation. This value depends on the variability of your system.