The poster is talking about using symbolic math to obtain a closed-form expression for the Jacobian that is then numerically evaluated. This will often be faste

The poster is talking about using symbolic math to obtain a closed-form expression for the Jacobian that is then numerically evaluated. This will often be faster and more accurate. For example, if your function is sin(x), then the symbolic math tells you your derivative is cos(x), so you put that expression in your code and compile it. When calling this on the angle x = 0.123, your code then just evaluates numerically cosf(0.123), rather than (sinf(0.124) - sinf(0.122)).